Is there a way to heal between attacks?

Attacked a few gyms today. Found that if I exited the gym and healed my mon, I can't fight again for a while. So I had to stay in the gym, and pick different mon, or use the damaged one again. Of course, as motivation drops, it's easy to use any old mon to beat down the foes, but it seems so pedestrian.

So I guess you need a Lapras to start taking down a D'nite, and then maybe Jynx or Cloyster or Piloswine to finish him off. But there will never be more than one in a gym at a time, so that's all one needs, except for raids, where one would need six pretty potent attackers.