Like the concept of predeterminism (is the future already written?), the concept that this might all be a simulation has exactly the same "solution": Don't get too hung up on it. We might as well act like it isn't.
We have as much control over things whether this is all real or not.
Do what you can to get by with as little harm as possible to yourself and others until, well, you know: Game over.
If you have the strength and maybe resources, you might even be able to make this existence more pleasant for others, but if not, try not to worry about it.
As for brain chemistry, I've been in the same head space that brought about your question, and undoubtedly will be again at some point in the not too distant future.
It's probably only because I've taken a bath today and put on fresh clothes that I'm relatively chilled out and philosophical right now. Also the Sun is out, which is probably helping too.

