How do I interrupt effect which is created by event

Hi guys! I'm very embarrased to ask such kind of question but I need your help.

The problem is in a battle system which i'm trying to design in a platform game. From the first time when animation has started to play, my hero began to loose hitpoints. What I need is to loose hitpoints "during the time", when animation is playing, but not after the first time when it was started to play. SOS please!

Is this way is the best one in my situation?

I think it's a good idea to use the variable. But is it necessary to use overlapping? You events may be triggered way too often. Have you tried the on collision event?