Does anyone know what's going on?

I think I am losing my mind or something and I want to know what's going on. Late at night I always tend to feel desolate, hopeless, scared, empty, sad, and just overall depressed. I am find during the day though and I don't know why I get like this at night. I do have social anxiety problems, but I am at home so that isn't the problem, or at least I don't think it is. I haven't seen my girlfriend in a few weeks and I guess I'm worried I'll mess things up between her and I, could this be a cause of it? It tends to happen late at night when I'm in my room and no one's talking to me, I don't like this feeling at all and I want it go to away. Please help?