Even if you have a relaxed day with no significant exercise or mental work, you still need to get sleep.
Learning – Your brain consolidates memories during sleep and you need a night’s sleep to really learn something. Memories are transferred from short-term to long-term storage during sleep and both factual knowledge and physical skills are learned in conjunction with sleep.
Creativity is also enhanced by sleep. Not just for artists, but people in general can come up with better ideas after a night’s sleep and with adequate sleep. You can think harder and more clearly when rested.
People also are in better moods after a good night’s sleep and sleep deprivation makes you grumpy.
The effect on mood is not just due to our general tendency to feel better when we feel stronger. It has been shown that the changes in brain chemistry after sleeping are similar to changes after taking anti-depressant drugs.
Cardiovascular impacts - the downtime of sleep allows your muscles to get some serious rest, and that includes your heart. During non-REM sleep your heart rate and blood pressure drop. If you don’t get enough sleep, you experience less time in this relaxed state and over time are at a higher risk for stroke, angina, and heart attacks.
Insufficient sleep puts your body under stress and results in higher levels of stress hormones in the bloodstream. Chronic low-level stress is associated with atherosclerosis in the long run.
The immune system is stronger when we get regular sleep. Regular short sleep makes you more susceptible to infectious diseases. Cytokines are produced in spades during sleep. The effectiveness of the flu vaccine is lower when we get insufficient sleep.
Sleep duration is also connected with body weight. Indeed, there is speculation that the accelerated lifestyles of recent decades have resulted in less sleep which has contributed to increases in diabetes and obesity rates. During sleep the body produces the appetite suppressing hormone leptin. The counterpart in the hunger system, the appetite-increase hormone grehlin declines. This effect, plus the general decline in daytime energy use, tend to make us fatter.
If sleep is a skill and if we can take measure to improve our sleep, the question arises: what should you be aiming for? What sleep goals are worth pursuing?
We want sleep to be
Come quickly after we get into bed or try to sleep
Be uninterrupted - a rule of thumb is that sleep efficiency under 80% is considered poor
Refreshing – leave us restored, both physically and mentally
Uplifting – leave us in a better mood
We want to minimize
Sleep inertia – how fast it takes to wake up fully in the morning
Sleep latency – time taken to get to sleep when first
Number of middle-of-night awakenings
Length of awakenings
Discomfort – sweating, labored breathing, temporary paralysis
Sleep efficiency can be measured with polysomnography, or even an EEG. An efficiency can be measured as a percentage (time spent asleep divided by time in bed).