Just wanting to sleep is understandable especially considering your current stress levels, often times many if us will find something comforting and something that never changes like a child would with their teddy bear,
Existential thoughts have always been a huge part of my OCD/anxieties and while I haven't overcome it yet(I've only just started working on my OCD actually) I just wanted to offer my support x I get through mine through distractions at the moment but i find replying to the questions helps,
So nobodies sure of the meaning of life or where we go when its over, so what? for whatever reason I was blessed with this life and I'm going to enjoy every crazy second of it, I personally feel like the meaning of life is different for every person, we find it and it could be a number of things, its important to remember that it was only curiosity before and it didn't bother you all that much so why would it now?
it is hard to say whether you would actually have existential depression especially as it can only be determined by professionals but all I'd like to point out is the mind is a powerful thing and if it sees something it can create the illusion and manifest itself, the same as if you tell yourself your banana milkshake is strawberry so much you can actually taste a bit of strawberry x
I know this was a lot of just rambling but I hope things start to look up for you soon!
All the best