How do I get over a slump?

I don't know what's wrong with me. At times I can be really happy, excited, I'll talk fast, and I want to do things. But lately I've been staying up way later and sleeping too much. I don't hang out with friends, I don't really have them. I feel nothing, worthless. I want to do nothing, I have no interest in anything. All I usually do is stay in my room. I want to be happy, I want to be nice. What's wrong with me?