In Phase 1, you have an alarm reaction, as your sympathetic nervous system is suddenly activated. Your heart rate zooms. Blood is diverted to your skeletal muscles. You feel the faintness of shock. With your resources mobilized, you are now ready to fight back.
During Phase 2, resistance, your temperature, blood pressure, and respiration remain high. Your adrenal glands pump hormones into your bloodstream. You are fully engaged, summoning all your resources to meet the challenge. As time passes, with no relief from stress, your body's reserves dwindle.
You have reached Phase 3, exhaustion. With exhaustion, you become more vulnerable to illness or even, in extreme cases, collapse and death.