General adaptation syndrome was first discovered by Hans Selye, a Canadian scientist that studied stress for 40 years. Selye discovered the body has an adaptive response to stress, he called that the general adaptive syndrome, and saw that GAS had 3 phases. In the first phase, you experience an alarm reaction due to the sudden activation of your sympathetic nervous system, such as you suffer a physical or emotional trauma. This causes your heart rate to zoom, blood gets diverted to your skeletal muscles, and you feel the faintness of shock. This makes you have your resources mobilized, preparing you to fight the challenge during the second phase, resistance. In the second phase, your temperature, blood pressure, and respiration remain high, but there's also a sudden outpouring of hormones. If this continues, this stress might eventually deplete your body's reserves during the third phase, exhaustion. When you are in the third phase, exhaustion, you're more vulnerable to illness, and sometimes also collapse and death.