Even if you're unemployed, even if you're taking time off from school, even if nobody is calling and making plans with you, get out of bed, take a shower, put on clean cloths, wear some cologne or perfume, turn all the lights on, do some laundry, clean up a little bit.
Doing all this stuff causes a shift in your perspective. Do it in spite of your situation. That's the only way to create sustainable happiness, because if your behavior is dictated by your circumstances, you're always going to be miserable. Don't let the world determine your mindset. Let your mindset determine how you view the world.