How does the Combat Medic Perk in Fallout 4 work?
As per this Fallout 4 Perks Comparison Guide:
Combat Medic (heal 100 points if health falls below 10%; can only be used once each day)
This says to me that in the instance your health drops below 10% then you will gain 100 hit points up to a maximum of one time per day.
Well, as tooltip says, health should restore as soon as your health drops below 10%. However, it seems that this doesn't work, at least I can't get 100hp heal from falling damage. Probably, perk is bugged right now.