What\'s Going On?

I don't know what is going on with me. One minute I am happy and the next minute I am sad. Last week, I was happy and now this week I am sad.  My mind is not as sharp as it use to be. I am afraid that my mind is slowly deteriorated. I feel worthless, and useless. I feel that no one cares about me. I feel so alone that I would rather stick myself again. I am so drained that I can't focus on life.  I don't know what to do anymore.