feeling worried?

have you ever been in a situation where all of a sudden you felt worried over something that you don't know. has it got to do with your mental imbalance? well, once in a while, i do felt that kind of worriness whether i'm at home, office, outdoor, with friends or without friends. whenever i'm in that kind of situation, i kept thinking very hard to find out what is the worries all about. the worries seems to relate to me very much rather than my family or friends. at the end, i just can't think of anything and i'm sure i pretty much thought of all possibilities. could it be my sixth sense telling me something bad is going to happen? i seriously don't know. that kind of feeling only last for a couple of hours or sometimes couple of minutes and it's all gone.