The process
Sleep is a complex process in the brain which is affected by lots of internal and external factors. The entire sleep process, from going to bed to getting up, can be divided in four phases:
1. The preparation
2. Falling asleep
3. Sleep
4. Waking up

1. The preparation
Yawning, burning and heavy eyelids - these are clear symptoms that you are getting tired. It is how your body tells you, after a period of mental and physical activity, that it needs rest.

2. Falling asleep
We slowly become less aware of our surroundings. A distinctive characteristic is that quick eye movements switch to slow, rolling movements. When we fall asleep our body temperature decreases. To make this happen our body releases water (transpiration) which evaporates on the skin. That is why adequate ventilation of your bedroom, mattress and bed is important.

3. Sleep
Sleep itself consists of several cycles After each cycle there is a transition stage, during which we wake up momentarily. On average we wake up about seven to ten times every night, usually without being aware of it.

Within each cycle of about 1.5 hours, you go through the following 3 phases:
- Light sleep: The first stage of sleep is light and short.  You only go through this stage a few times every night. When you get to this phase for the first time, your thoughts slowly subside and your muscles start to relax.  Then your heart rate slows down and your body temperature drops.
- Deep sleep: After about 20 minutes your body and brain become extremely relaxed. At his point your brain activity reaches its lowest point. This stage is also referred to as 'deep sleep'. During this deep sleep the chance that you wake up spontaneously is only small and you will be difficult to wake. Deep sleep is very important for your physical and mental recovery and health.
- REM sleep: After about 30 minutes in deep sleep something strange happens: your brain and body move quickly, instead of relaxing your heart rate accelerates, your breathing becomes superficial and your eyes jump from left to right. You are now in your REM sleep - named after these Rapid Eye Movements. This is also the phase when you have dreams. You wake up momentarily and you start a new cycle and go through the different phases again.

4. Waking up
In the early morning hours proportionally less deep sleep phases occur, allowing for the transition to waking up to take place more gradually. When you wake up, your body temperature rises. Your body does this, as if your biological clock were switching on the heating.