Deep sleep, or slow-wave sleep, has a restorative effect on our bodies - helping us to fight viruses and feel refreshed the next day.
But what is deep sleep? As we sleep our body cycles through four different stages of sleep, and after two stages of light sleep our bodies finally fall into a deep sleep. We need up to 2 hours a night of deep sleep to feel ourselves the next day, but some factors can stop us from reaching that state.
