In animal sleep, a sloth sleeps 20 hours a day while a porpoise sleeps half a brain at a time. Birds do not sleep and rabbits and squirrels sleep 10-14 hours a day. People need a wide variation of sleep and can range from 1-10 hours a day. There is more need for sleep at birth, while as we age our sleep needs are less and lighter.
Sleep problems are a common symptom for people who are recovering from traumatic events.
One's usual methods for falling asleep may no longer work. Disturbing thoughts of reenactment, rescue or reunion may interfere with one's sleep cycle. Nightmares and sleep terrors occur in response to adjusting to shattered realties. No reading or watching TV in bed. These are waking activities.