You know, it might be a good idea to RTFM. There is a button to push that activates the Predator's health kit. You get full health instantly, but must have more than half of your energy left. The health activation takes half of your energy away. But the good thing is that there's also a button that allows you to instantly refil your energy -but you become uncloaked and cannot move faster than a walk or basic jump.
In other words, find a place to HIDE. Heal yourself, replenish your energy, then cloak and get moving again.
See what happens when you pay attention? You enjoy the game
nik