Researchers have difficulty agreeing to the amount and duration required to have us function at optimum levels. Most research involving rest is done in the field of sleep studies. Insomnia is frequently stress related. When we sleep is very important. Most of our activity takes place according to a circadian cycle, slightly longer than 24 hours.
Sleep normally occurs during the time of reduced physiological functioning.
REM sleep peaks during the early morning hours when our body temperature is at its lowest. If we work late hours and stay up half the night worrying, we are likely to sleep but miss some of the rest needed from REM sleep. Serotonin is a brain neurotransmitter that has been linked to sleep deprivation and stress. When serotonin levels are low we are likely to experience depression, fatigue, and frustration. Resting does not necessarily mean you have to go to bed and sleep.