Your Max Health is low compared to the boss's. Increase Max Health to take and deal more damage per attack. come on my health is 25,600.i dont think anyone else is even at that(maybe close but i doubt at that)
What is the health of the boss that you are fighting? Right now I think it is just a set percentage based off of the boss that you are battling, if you are lower than that percentage then that warning will show up regardless of how much health you have.