The three stages of general adaptation syndrome, commonly known as GAS, include alarm reaction, resistance and exhaustion. GAS refers to the physiological changes that occur in the body in response to stress.
Hans Selye first proposed the theory that all types of stress, whether physiological, psychological or environmental, can trigger a series of typical bodily reactions. Alarm reaction, which signals the first phase of GAS, refers to the instantaneous feedback when the body is subjected to a stressor. The "fight or flight" response is an example of an alarm reaction. During the second stage, the body starts to normalize by adapting to the stressor, but remains on heightened senses. Cramming for an exam is an example of this stage. When the body reaches the point of exhaustion, it can no longer adapt to the stressor and often results in a nervous breakdown or even death.