What is sleep and why do we do it? It may at first seem glaringly obvious, but the question of sleep is actually quite mysterious. In simple terms, it is an extended bout of rest we experience on a daily basis, where we most often lay down with our eyes closed. But there’s more to sleep than meets the eye.

The average person spends around a third of their life asleep. In this time, our bodies are able to replenish energy stores and make repairs, while our minds organise and store the memories of the day before. The amount of sleep you need depends on your age, sex, health and other elements, and sleep cycles change as we grow older.

However, here is a general guide.

• 1-12 Months Old: 14-15 Hours Per Day
• 1-3 Years Old: 12-14 Hours Per Day
• 3-6 Years Old: 10-12 Hours Per Day
• 7-12 Years Old: 10-11 Hours Per Day
• 12-18 Years Old: 8-9 Hours Per Day
• 18-65 Years Old: 7-9 Hours Per Day
• 65+ Years Old: 7-8 Hours Per Day

The Sleep Cycle

When we first fall asleep we enter non-rapid eye movement sleep (NREM). This is divided into three stages, with each becoming progressively deeper. NREM1 and NREM2 are light phases of sleep, from which we can be easily roused. NREM3 becomes deeper, and if woken up, we can feel disorientated. Following on from this is rapid eye movement sleep (REM), the stage at which we dream.

Each sleep cycle lasts around one and a half hours, and in order to feel fully rested and refreshed when we wake up, we must experience all four stages. A full night’s sleep will include of five or six cycles, while a disturbed, restless night consists of fewer.

Ideally, our circadian rhythm will climb in the morning and make us feel alert and refreshed. It then peaks in the evening, and after being awake for around 15 hours, we will feel the pressure to sleep again. As the night draws in, our circadian rhythm drops to its lowest level, and we are able to close our eyes and fall asleep.