During the average session of sleep, a person will experience five proper sleep phases. This means that as you sleep, your body is actually experiencing different sensations through those five sleep phases.

The first of the proper sleep phases is... wakefulness! No, actually, this is more like phase zero. When we are experiencing wakefulness, our brains exhibit high brain waves, known as beta waves which allow us to consciously function day-to-day.

The first proper sleep phase is known as phase 1 sleep. During phase 1 sleep, our brain exhibits a combination of alpha and theta brain waves, and our bodies begin to relax and prepare for sleep. This sleep phase is commonly experienced while we are daydreaming, 'zoning out' or feeling drowsy during the day.

The second of the proper sleep phases is very interesting, it is where our brain exhibits sudden bursts of activity. Like the phase 1 sleep, people in the second proper sleep phase are still considered awake, and phase 2 is also a transitional phase into proper sleep. The brain is attempting to 'switch off' in preparation for proper sleep. If someone is awoken during the second sleep phase, then they often don't remember having fallen 'asleep'.

The third and fourth proper sleep phases are considered 'deep sleep' - this is when you're asleep and if you're woken up, you know you've been asleep. It is at this phase that the brain exhibits a combination of delta and theta brain waves. Our bodies physiologically adapt to sleeping conditions - we experience drops in blood pressure, heart rate and respiration, and our body repairs any muscle damage encountered during the day.

The final and fifth of the proper sleep phases is REM sleep. REM is an acronym for Rapid Eye Movement, and very little is known by the scientific community regarding the purpose or activity that occurs during this fifth proper sleep phase. Experiments conducted in the 1950s uncovered that when people were in this phase of sleep, their eyes would move very rapidly, and if woken up, close to 95% of people would report having been dreaming. Thus, REM sleep is also known as dream sleep. The brain exhibits extraordinary activity during this final proper sleep phase - in fact, it is the most active of the proper sleep phases.

And there you have it - the five proper sleep phases.