I'll think a bad thought at a random time and stop what i'm doing?

Here's how it works. I'll be doing things, be it doing work, playing online, or just plain laying around and being lazy. All of a sudden I have this thought just randomly pop into my head! Not just any thoughts either. I'll think of bad things that happened in the past, something me or someone else said in recent, and numerous other things. Then I just stop what I'm doing and go into this often very short, sometimes long, freak out mode. I begin to worry about said subject. I'll get up and walk around while thinking about it. I sometimes begin talking to myself and even cry as well. Is this bad?