I'm usually a calm diver but I once had the combination of a slight ear infection and a speed boat passing overhead. This combination of mild pain and an ever increasing high pitched whine convinced me that my eardrum was ruptured and was rapidly getting worse. I did an emergency ascent from about 8 metres and luckily didn't have any nasty side effects.

As a diver you are usually calm and rational when dealing with expected risks (low air, bad visibility, etc.) but anything unknown or unexpected can trigger panic.

A friend of mine is a commercial diver and he has stories of seasoned co-workers panicking for extremely weird reasons.