Forty years ago, the US Air Force and NASA tested the ability of sleeping pilots to wake up and immediately take flight. They found that even the most expert pilots made inexplicable mental errors. Scientists discovered that the mistakes were caused by the extreme grogginess of waking from deep sleep. This impaired ability to transition from sleep to wakefulness was named “sleep inertia.”

Sleep inertia is the extreme grogginess experienced immediately after waking up, especially when woken from deep sleep. If woken when the brain is less active during deeper sleep, it will take more time to feel alert. If woken from lighter sleep, however, the transition from sleep to feeling awake will be considerably shorter.

Sleep deprivation both causes and compounds sleep inertia, and because over 150 million Americans do not sleep enough, this condition is a significant health concern. Sleep deprivation or sleep inertia have been directly linked to several tragedies including the Exxon Valdez oil spill, the Challenger space shuttle explosion, and the Three Mile Island nuclear disaster. Closer to home, The National Highway Traffic Safety Commission reports that over 100,000 crashes and $12.5 billion in property loss occur annually as a result of drowsiness.