Wake them up during REM sleep and ask them if they have been dreaming. Wake them up during NREM sleep and ask them if they have been dreaming. Ask them under hypnosis if they have had any dreams recently. Bats are a relatively more primitive species. Bats are a more highly evolved species.
People sleep about as long after an inactive day as after a vigorous day.
Prolonged sleep deprivation leads to irritability and impaired concentration. Certain stimulant drugs can interfere with sleep. Just before a person awakens. When body temperature is at its lowest. When body temperature is at its highest.