Do something that would make you happy. Take a walk, read a good novel, watch something funny, listen to good music, doing sport, eating, etc :D

I think you should talk to someone you are close to. Maybe this might help you figure out why you feel this way. You should also surround yourself with fun, positive, and good people. And Remember to smile, okay? Hope this helps!! :)
(Hahaha... Fault In Our Stars reference: okay? okay.)

Read something fun. Released your stress with something that will make you happy. If you're having problems, try to solve it. If it related to people surrounding you, discuss and solve it.
Anyway, everyone have mood swing, either it bad or not!
Cheer up yourself with someone who is cheerful.
Keep fighting! ^^

i think you're in depressed of something. share your problem with others and let them cheer you up so you will able to handle your problem. listening to music (but not the sad one) when you feel down. last time i felt i bored of anything i read all the blogs here, and i saw there are many people are suffering from their problems too. i talked to some of them just for asking their condition and somehow i felt better. *shrugs*