windshield wiper loose on post

Today I was driving in the rain with my front wipers going. Suddenly for no obvious reason, the driver side wiper went beyond it's normal range, eventually moving all the way off the windshield. I pulled over and was able to push the wiper back to it's stand-by position. But I shouldn't be able to move the wiper at all. It's now completely loose and moves randomly. Any help?

If there is a small plastic cover over the base of the arm, pull it up and tighten the bolt that holds the arm in place.

If there is a small plastic cover over the base of the arm, pull it up and tighten the bolt that holds the arm in place.

My father in law actually did exactly that and it took care of the problem, but I sure appreciate the help!!

I think usually caused by turning wipers on when frozen to windshield.