How to sleep deeply 

Scientists agree that sleep is essential to health, and while stages 1 to 4 and REM sleep are all important, deep sleep is the most essential of all for feeling rested and staying healthy. The average healthy adult gets roughly 1 to 2 hours of deep sleep per 8 hours of nightly sleep.

Insomnia has many possible causes, including stress, anxiety, depression, poor sleep habits, circadian rhythm disorders (such as jet lag), and taking certain medications.