How do you get yourself back up on those terrible days?
It really helps to get up and move around even if you don't feel like it. Also, it's generally better to be around people. Since it's almost Halloween you can put on an outrageous costume and go to the mall and find out what kind of reactions you can evoke.
If you absolutely can't find anything to do, then you can go to Walmart and pretend you're a greeter. It's Friday night so you know it's going to be special.