Tom elaborated on this much more through several interviews (many of them Live Q&A) spanning from after Thor’s release in 2011 to as far forward as Ragnarok; and each time, the answer was roughly the same. In 2013, the most precise answer prior to and without giving away Thanos’ reveal was dropped on stage in one such LIVE Q&A, which you can still watch on youtube and will be linked below.

Marvel's Thor: The Dark World -- Exclusive Presentation + Q&A with Tom Hiddleston LIVE on stage. Tuesday October 8, 2013, Event Cinemas George Street, Sydney.

Audience [Q:] “What happened to Loki when he fell into the void? What did he experience?”

Tom [A:] “I think he went, like, with everything else to—Joss Whedon and I discussed it—to a sort of… It was just, like, the worst place imaginable. I think he went to sort of all of the darkest recesses of the universe. I’m sure he had a brush with— several brushes with death. “

“ I think he ran into the shadiest characters you can find in the nine realms. I think he had to rely on his wits to protect himself. It was really, really, really unpleasant, I think. And all I have to— I don’t have any frame of reference for that, really: except for imagining what it might be like to be kidnapped by a terrorist cell or something; and have to survive a very, very frightening and precarious existence. “

“But whatever it was, it was important when Loki came back for the Avengers that whatever compassion he had left was absolutely shriveled to a minimum because of the experience that he had. Harrowing, I think, and scarring for life—in a way that Thor and Odin and Frigga find very, very difficult to understand.”

https://youtu.be/VdfobYiZsVk?t=1069 (timestamp 17:50)

Tom, Whedon, Branagh and the creators were so solid on the fact that he was tortured and coerced, that the life threatening horror and Loki’s experience being compared to ‘The Seventh Circle of Hell’ while with Thanos is the most consistent reference over the course of YEARS of interviews.

Here are the most notable quotes from Tom himself. I don’t have all the links readily on hand, but hey if I could use google to find them back in the 2010s when I first started REALLY delving into his MCU persona to outline Lokiverse .. so can you, today. I’m just copy/pasting this out of my off-sreen references doc. I think the most interesting reference Tom makes for me (and one I play with sometimes if not a lot in Lokiverse) is the fact that he states Loki is 'undercover' at least once through some of these interviews...

“[Joss and I] talked about it a lot. We talked about this idea that Loki disappears through that wormhole of space and time, when the Bifrost is destroyed, and he kind of goes through the Seventh Circle of Hell. And he’s on his own. He’s on his own in the dark corners of the universe, and the journey he goes on is pretty horrible. It’s like getting lost in the rainforest or something. You’re going to come out the other side a bit mangled on the outside, and on the inside. And he’s made this deal with Thanos and the Chitauri […] and he’s being played too, by them. But I just think it’s interesting, actually, because we’re more interested in what that does to him as a character, because it gives us a justification for his increased menace. […] He’s much darker, and more scarred.”

“What happens in the space between the end of Thor and the beginning of The Avengers is Loki’s made some very shady deals with the gangsters on the streets of the Nine Realms.”

“In Thor, Loki is a prince of Asgard. But by the time The Avengers starts, Loki’s been around the block of the universe. He’s met some shady gangsters and he’s gone undercover and he’s come back looking a bit meaner.”

“Working with Alexandra Byrne, who was the costume designer again, saying: let’s take the regality of the lost prince of Asgard, and make him a damaged pirate, so there’s evidence of some kind of experience beyond what happens at the end of Thor. And then talking with Joss about his evolved psychology and how, in the space between the end of Thor and the beginning of The Avengers, Loki has gone through a whole bunch of stuff which will register on his mind and on his body and will change who he has to become. It’s really exciting!”

“I think somewhere between the end of Thor and the beginning of The Avengers, Loki has been to the Marvel equivalent of the 7th circle of hell. At the end of Thor you see him let go. He lets go of the spear, he lets go of Asgard, and he lets go of the need of his brother and father’s affection and approval. He has bigger plans now.”

“[He’s] more mischievous. More evil. More hubristic. More delusional. More damaged. More badass. He doesn’t want revenge so much as identity. Belonging. Purpose. Self-esteem. Through delusional dreams.”

“The back story for us was that when Loki lets go of that spear at the end of Thor he is doing it both literally and metaphorically, he’s letting go of his affection for Asgard—his connection to it, his need for Odin’s love, and he disappears into the wormhole. The audience thinks is he dead, but where he’s gone is he’s sort of been to the seventh circle of hell and back and along the way has met these aliens and made a shady deal with them and they’ve found the Tesseract. Loki was brought up with the expectation of entitlement—he was born to rule, both Thor and Loki were born to be kings. And yet, there is no kingdom for Loki, so he has to find one. So he’s come down to earth to subjugate humanity and rule the human race as their king. I guess we’ve skirted over the facts of where Loki disappeared to, but we’ve imagined that he’s had a pretty horrible time and this is his kind of last chance at giving himself an identity or a home, somewhere to belong to.”

Just a quick tidbit to think about when passing over the words Seventh Circle of Hell, this means Tom [and creators] were equating his experience to any and all of the following:

Being eaten alive by Harpies.

Being eternally chased and ripped apart by dogs.

Being in a desert of burning sand, and assaulted with fiery burning rain.

In other words, in no means whatsoever, was he as the muse quote above has said, offered ‘tea and sugar cookies, as a persuasion tactic’. Which, even taking Loki out of the equation: fits everything we know about the character he was forced to deal with, and in Tom’s own words (and very obviously to us now of the eco-variety but still) a horrifying terrorist. A character who, very much was murdering half-planets at a time: murdering Gamora’s mother and half her own planet when she was still a small girl as just one example of direct genocide, and Drax’s wife and daughter through Ronan as one example of indirect genocide being carried through.

From the Gaurdians of the Galaxy, we also know just how much this man values and treats even those he claims as family (never mind strangers not a part of it, or not yet a part of it) through Gamora and Nebula’s dialogue: which lets face it just further supports his Mad Titan title (that’s Mad as in out of his freaking mind if you didn’t know.)

"My father would have Gamora and me battle one another in training. Every time, my sister prevailed; my father would replace a piece of me with machinery, claiming he wanted me to be her equal. But she won. Again, and again, and again, never once refraining." - Nebula to Obfonteri GotG2 ( https://youtu.be/PYIrtpEq3Xs )

“Nebula! I was a child like you. I was concerned with staying alive until the next day, every day. And I never considered what Thanos was doing to you. I'm trying to make it right. There are little girls like you across the universe who are in danger.” - Gamora to Nebula GotG2 ( https://youtu.be/DdTN4kW2O8Q )

"You kill and torture and you call it mercy, the universe has judged you. You asked it for a prize and it told you no. You failed. And do you wanna know why? Because you love nothing. No one." - Gamora to Thanos : Infinity War

More references to just how great things were in Thanos’ camp even for the ‘friendlies?’ Examples why the sane (or even semi sane) got out as soon as they could with Thanos as a target instead of fond memories and loyalty and all that jazz? Sure!

Let’s not have a look at the Other, though (that one you can find everywhere and is blatant enough a creepy, sadistic torturer: but yes, there’s more!;) and instead look at Ebony Maw, who tells us exactly the twisted mentality with which Thanos deals with everyone: and, if you've picked up especially even Maw's inflection at the prospect of being 'judged' by Thanos should he so much as still have Stephen attached to the Time Stone, as one of his most trusted as well as his crier.. yeah creepy, sadistic, murderous.. and, well. Read on..

"Hear me and rejoice! You have had the privilege of being saved by the Great Titan. You may think this is suffering. No... it is salvation. The universal scales tip toward balance because of your sacrifice. Smile... for even in death, you have become children of Thanos." - Ebony Maw to the defeated, dead and dying Asgardians on the Statesman : Infinity War

"Hear me, and rejoice. You are about to die at the hand of the children of Thanos. Be thankful that your meaningless lives are now contributed to the balance…" - Ebony Maw to ..pretty much anyone listening in New York (Stephen, Wong, Bruce and Tony) : Infinity War

"In all the time I have served Thanos, I have never failed him. If I were to reach our rendezvous with the Time Stone still attached to your vaguely irritating person, there would be ...judgement. Give me... the Stone." - Ebony Maw to Stephen Strange aboard his deployment ring : Infinity War

So.. no. We have every reason, example, and in-character on-screen testimony from those closest to and inside that circle; to believe what we’ve been told outright in those interviews in regards to this period in his official marvel profile, even after Gagnarok; is the period they were talking about in his official profile on their sites (recently very mildly updated to reflect this AND other effects mentioned here and in other threads,) for years: which also states outright in addition to that, it is a fact that the Scepter and Mind Stone inside it is also used to manipulate Loki’s mind and emotional state during the entirety of Avengers to get that result:

Official Marvel Profile (chrionicles):

“ Devastated that the Allfather could not see his actions were for him and Asgard, Loki lets go and falls into the abyss.

Arriving at the Sanctuary through a wormhole caused by the Bifrost, Loki met the Other, ruler of the ancient race of extraterrestrials the Chitauri, and Thanos. Offering the God of Mischief dominion over his brother’s favorite realm Earth, Thanos requested the Tesseract in return. Gifted with a Scepter that acted as a mind control device, Loki would be able to influence others. Unbeknownst to him, the Scepter was also influencing him, fueling his hatred over his brother Thor and the inhabitants of Earth. “

As for the original link to the fact that Loki’s arrival was toned down: I don’t have that interview handy (though I’m sure someone can and will find it, or will link something if they have it and see this).

But, what I do have right on hand that was part of that interview and why it came up in one; is the original concept art: and it’s even more telling of just how polite Tom is/was being with his wording in those descriptions too. (as usual and as we all know; he's a sweetheart) If you would like to look it up, the artist is Andy Park.

You can search ‘Avengers Concept Art Andy Park’ and probably find at least one article where they talk about it but, here... have a look for yourself at what the intended visual was that would have changed Avengers’ rating:

But especially, this below was the more detailed view of how Loki looked on arrival in the Dark Energy facility on Earth in the first Avengers, before it was toned down to keep the rating:

...yeah, they could not keep the PG-13 rating with that kind of gore in their opening scene.