I just recently got home from a solo vacation that I had been wanting to do for months. It was great in the moment. But the feeling feels so fleeting. As soon as it was over, any bit of joy I felt then, is now a distant memory. It's almost as if the few days I spent away meant nothing. I'm back to feeling uninterested and numb. 
I've been in bed now since I've gotten home. Mostly because I have no interest in anything. I don't watch TV. I don't play video games anymore. I don't read anymore. I stopped playing guitar. What do you do when nothing interests you? How do you keep pursuing a hobby when it doesn't bring you any enjoyment, only frustration? It's honestly driving me crazy. I feel like I'm just existing for the sake of it without any meaning or fulfillment. How is this even living?

TL;DR: Nothing interests me. I feel no enjoyment from anything. I'm just wasting away. What am I supposed to do?