The other shoe...

Ever have that feeling that you are waiting for something bad to happen? I have been having a strange nagging feeling for the last four days. There is nothing apparently wrong. There is not obviously out of order. I just have a weird sense of foreboding.
I can be fine and all of a sudden get very nervous and jittery. If I didn't know better I would say I had a guilty conscience about something, but I haven't done anything that would be bothering me.
I hope it goes away soon - it's freaking me out.