Sudden feeling of intense nihilism

I've been dealing with some depression for the last few months.

 Yesterday after work I was hanging out with my wife, we talked a lot and I was feeling kind of manic. Usually I just crash when I get home from work and sit on the couch for hours until bedtime, but last night I showered and had some caffeine, then we started talking and didn't really stop for a couple of hours. I started feeling really hyper focused, like if I had taken a stimulant, and was pacing and fiddling with stuff. I also had a few drinks after a couple of hours of this. Now today I feel extremely nihilist. 

I'm not sure if that's the right word to use, but I just literally don't care about anything. I don't care about eating. I don't care about my job. I don't care about my relationships. I just feel extremely neutral. Like I just want to exist and not care about anything and be left alone to do whatever.

 It's a really strange feeling and was wondering if anyone could relate or had any advice.

Maybe it's some sort of disassociation. Idk.