We need 8 hours sleep per night. Fatigue is defined as “a physiological state of reduced mental or physical performance capability resulting from sleep loss or extended wakefulness, circadian phase or workload (mental and/or physical activity) that can impair the crew member’s alertness and ability to safely operate an aircraft or perform safety-related duties”. Fatigue is a physical, not a psychological, state. The only remedy for fatigue is sleep. Sleep allows the brain to clear toxic chemicals and replenish energy stores, and also allows memory consolidation. Several factors contribute to how and when we sleep, including the homeostatic sleep drive (sleep need), our biological clock and its effect on circadian rhythms, and our sleep urge. If we do not get our 8 hours of sleep every night, we accumulate a sleep debt. Chronic sleep debt results in the brain downgrading its activity. Sleep strategies can mitigate fatigue risk