A sleep cycle generally consists of four stages of sleep:
Before sleep, a drowsy stage when you begin to feel tired.
Light sleep, which is a stage where you’re dozing off, and your body is slowing down and preparing for a deep sleep
Deep sleep, when our bodies experience rest and restoration. Deep sleep is said to be essential to a restful sleep. You may find it hard to be woken up when you are in a deep sleep
REM or Rapid Eye Movement sleep. During this stage, your brain is active even while you experience rest. This is often associated with vivid dreams.
Good quality sleep — which includes deep sleep — is restorative and important to your wellbeing. There are things you can do that help you experience good quality sleep more often.