Sleep is so important for the recovery of the mind and body. The more exercise is performed, the more sleep is needed. When we have a lack of "deep" (non-REM) sleep it results in a person feeling physically tired. When we have a lack of REM sleep, it causes us to feel anxious and irritable. Various hormones are secreted into the body during sleep. Sleep serves important immune system functions and memory. Sleep plays a big role in the healing and repair of the heart and blood vessels. When we are chronically sleep deprived, we are subject to an increased risk of heart disease, kidney disease, high blood pressure, diabetes, and stroke.

Studies have shown that a good night's sleep improves learning. When you sleep, your brain forms neural pathways to help you learn and remember information. Because of the changes in the brain due to lack of sleep, one may also experience trouble making decisions, controlling emotions, and coping with change. Lack of sleep has also been linked to depression and suicide.

A lack of sleep also increases your risk of obesity. When you are sleep deprived, your body produces more ghrelin (the hormone that makes you feel hungry) and less leptin (the hormone that makes you feel full). With every hour of sleep lost, your risk of obesity goes up.