So just to throw our some real numbers.
I'm a 18str/16con fighter, 21 hp, 18ac
During our last fight with the BBEG I took a total of 88 HP in damage
I recieved a total of 33 HP in temporary hit points
I recieved 33 hp in healing and a second wind
I ended with 9 hp
I was down to 2 or 3 hp...