Controversial opinion but I think that Levi being concerned that the others will forget about him here
Armin: It's reckless
If (you) don't sleep/(lie down) some more
Levi: ..sleep some more you say?
If I sleep any more than this you guys are probably going to forget my existence
To clarify, there is a certain amount of anxiety he has here, but it has more to do with the fact that he is not in a shape to fight in an upcoming battle that he figures, knows strategically that every hand on deck will be needed, and yes, he wants and needs to be useful now, but it's not that he literally thinks that they will forget about him if he isn't.
In other words, that it's like this:
oh heck that's omaera aka a plural you there XDD
We didn't spend all this time learning that his words need an interpreter (thank you Hange) only to then go and take his words literally.
And I mean, put that together with
...if I still have two fingers it's enough
(there's/it's) no problem
and I think that it matches up to the idea.
As an adjacent to this topic, I'd also like to point out once again that there's a lost in translation here, or rather, there was a subtlety that wasn't noted and never went into the translation here:
お前ら…図体ばっかりでかくなりやがって…
You guys.. only your bodies are getting bigger(I am full of hatred in my heart modifier)...
So there are two subtleties here, the second of which was noted by the translator and an attempt was definitely made to put it in writing:
However, the "only" part was missed and I believe a few fan translations have it, however also, even translating it as "only" is not enough, there is a nuance to it and a couple of other "only" words that I've explained here, the one used is the first one, written as bakkari here and bakari in my explanation.
Here's the dictionary link for the term, and I have to say that I'm rather intrigued by this translation in it:
口ばっかり!
You're all talk and no action!
because, you can see that the japanese is pretty short, and indeed it really is the first part of it, the "you're all talk" bit, or literally, "nothing but mouth". But like I said, there is a subtlety with this version of "only" and it is the implication that there are other options or possibilities one could have or have gone for, however, this is the option taken, or the only thing being done, sometimes again and again. The other subtlety is that there is a judgement value being taken on it. And so, I feel like this translation truly reflects the meaning of the statement in saying the hidden part out loud XD
And so, what is the hidden value of what Levi is saying? And it's that "only your bodies, but not your minds, are getting bigger"
In other words, what Levi is saying isn't:
"you guys are getting bigger"
"you guys are as dumb/childish as ever"
which again, if you look at the panel, I think actually makes sense in the scene as something that he's responding to Jean's statement with, rather than being a comment that seems to come completely out of the blue and off topic. (Also, it's not "sorry about the heat", it's "thank you for your hard work in this heat", and I think you can see why I really don't wanna deal with the english translation except when I'm doing this sort of thing)
And like the first example, it's sarcasm. I'm sorry to all the wonderful Levi headcanons but it's canon that Levi can't say something nicely to save his life. And I also feel like things like these are being taken out of their context as statements to define the characterisation about Levi, and becoming some kind of new mythos. Yes, he is kind and concerned, and sometimes he hides that under his sarcasm, but also, he is just plain sarcastic sometimes, and those around him have known him long enough to understand what he means, that underneath his rude words, he really cares.
And I think that he knows that they care for him in return.
I honestly can't see him worrying about his place in the family of the Corps, grimly, I think he's jolly well sensitive enough to see the writing on the wall first, and thinking that they might not care for him would actually mean that he's thinking badly of the others, that he's so caught up in himself that he can't see what's actually around him, and that just doesn't make sense?
Anyway, these are things that are definitely starting to fall into the "sometimes things that are fanon are worse" category for me, also that "just because many people believe this doesn't mean it's confirmed" category and to top it off, the "just because it's the official translation doesn't mean it's correct" category too XD
(Usual disclaimers apply :)