There are different ways to do it. The way I did it in my mod (Amazing Follower Tweaks) is I monitor the player when combat begins. There is an OnCombatStateChange event that I use. Every time the follower switches targets, they quickly check the PC stats and if they are low, I manually apply the animation, sound and healing to the player using scripts. I also manually damage the NPC's magicka reserve. I even display a message with the followers name indicating they just healed the Player.
Now... you could also scan the area for NPCs other than the player. Probably would have to make a seperate quest that you start/stop so that its aliases get filled with potential heal targets (Teammate, GetActorValuePercentatage Health &--#60; 0.25, etc...) I didn't bother with healing other NPCs since most of them have healing potions.
If you make your own NPC, you can attach you own scripts directly to their actor record. Or you could simply make a mini-quest to manage them (injected as an alias).
Thanks for replying, and it sounds like you built a mod that works, but every bit of information I've found on these forums is like telling me, "If you want to get past that wall, just use the energy ray gun to blast a hole through it." Problem is, I don't know how to fire the energy ray gun, and the manual is written for people who have had prior experience.
Maybe if I read through the CK info enough times it might start making sense, but right now, nothing's sinking in.