Maybe you wouldn't had that issue if you were, say, a hockey player. Like your body is not prepared to be sitting in front of a screen ten hours a day or a whole shift poring coffee. I've been learning to get over that brain draining feeling by exercising and not just a running session at the end of the day (which really helps) but shorter intervals in the middle of the day. E.g., I had great success exercising every 5 minutes in my pomodoro technique breaks - huge difference. Not sure if that applies to everyone though.

Socializing is also really helpful for me, but it's hard to make quality friends - I am an immigrant which doesn't help at all.

On a side note, I always try to remember that happiness is a choice. Simply try. It takes some work.