Feeling Unreal and Disconnected from Reality

I think this is a derealization/depersonalization thing but I struggle to remember that death and other people exist. I forget that adults exist and that other people have jobs and not just my dad, sister and sisters fiance. every time I remember I'm gonna be an adult in a few years and think about how I'm gonna move out and get a job and stuff I start dissociating and feeling unreal. I have no idea what to do or how to cope. I constantly feel unreal and like I'm invincible. like I'm "the main character" of a book. every decision and conversation feels like it happened before. everything I do feels like it happened before. sometimes I feel like I'm floating when I'm just laying down and I have to constantly distract myself to keep myself from thinking I'm unreal. I don't know what to do. should I go to a mental hospital? idk what to do. I've been in one before and if helped a lot but it's the only time I get any form of therapy or anything. what do I do?