Tiredness is a state of the mind and/or body feeling the need for rest.
Stress is the non specific reaction of the mind and/or body to any demand. Stressors can cause just about everything from a fleeting momentary reaction (startle response) to a heart attack.
Fatigue is an extreme form of tiredness, often described as exhaustion. It can be acute or chronic.
Burnout, which is now referred to as compassion fatigue, especially among stressed health care workers, such as those in military settings at time of war, is a chronic form of tiredness that can interfere with the ability to function.
– AIS President Daniel Kirsch, PhD, DAAPM, FAIS