Hun, I'm going to say this with all the love in my heart. If you don't know what domdrop is, you may want to do a bit of research into the BDSM scene before doing any play for it, okay?
Sub drop is when a sub has like, I guess I'd describe it as an emotional or physical crash after a scene. Scenes can be very intense emotionally, mentally, and physically, so crashes after they're over can send you kinda spiraling into a bad place mentally/emotionally. Dom drop is the exact same, just with the Dom instead.
It doesn't happen every time, but it really sucks when it does happen. So, to mitigate the chances and to help everyone involved in the scene come down easier and gently, we use aftercare. This can take a wide range of forms, and what works for 1 persons aftercare might not work for anothers. Some of the common ones are like, lighting candles with calming scents, listening to playlists you enjoy, taking a bath or shower together, cuddling up under a blanket that has a good texture, talking about the scene together, massages, ordering some food or making some or just having a tasty snack, etc.
And not just in the immediate post-scene time. I've known people who tended to drop hard the day after, and so they needed reassuring messages and conversations to help balance it out and ease that coming down.
Gotta remember, BDSM all around is adults playing pretend or putting on a personal play in very intense ways, so we take steps to make all parts, from the build up, to the scene, and the events following it, as good as they can be for all the actors involved.