Unlimited health only sets it so that your health doesn't drop. As far as I know though, the max health the game will allow (short of editing) is like 825. At higher difficulties, abilities and weapons can do over 1400 damage.
So even with the trainer, you can die. It just prevents you from dying to small arms fire. But if you let a sniper shoot you in the head or hug a grenade, then that's on you.