There are two types of stress; adaptive, which is helpful to your body and your situation and maladaptive which is not helpful.
Adaptive stress is the kind that happens if you are faced with a thief pointing a knife at you. Your blood will flow away from your digestive system towards your muscles, your brain will become hyperactive, and your reproductive drive will shut down. Thousands of biochemical changes will take place in all the cells of you body within a couple of seconds, enabling you to defend yourself (fight) or run away (flight).
MALADAPTIVE (not useful)