It sounds like you're out of those Vitality Points. These points are used up by battles. The longer the battle lasts, the more vitality points you use. Some characters start with more than others. Find yourself a heal station and that will replenish those precious points. I had this same problem. It does talk about what these points are, and that it is bad if you lose them during the beginning of the game, but if you are like me, I kinda clicked right through them wihtout reading much. Check out the wikipedia article on the game, it talks about those vitality points under the Statistics and Points section.
http://en.wikipedia.org/wiki/Enchanted_ArmsHope this helps,
Popssracer