RE:What I'm askingThat's a valid question, one I've considered as as well. The answer is dependant on your time horizon and risk tolerence.
If you plan on needing the money you have invested within a short window of time (say 6 months) you may well want to pull your money out if you see something that bothers you in the overall markets. If you're looking longterm, (3-5-10years) just let it ride.
Most of all, don't gamble.