Climbers often notice that they do not sleep well and feel rested when in the mountains. What is often experienced is waking up several times. This results in broken nights. Fortunately, there is nothing serious going on. The cause, again, lies with the reduced oxygen tension. It causes the phenomenon of 'periodic breathing'. This means that a person does not breathe as usual, but in this case stops breathing for a while and then compensates this pause by breathing faster.
The body regulates breathing according to the concentration of two gases in the blood: oxygen (O2) and the waste substance called carbon dioxide (CO2). The concentration of these gases is measured continuously and precisely to ensure compliance with the normal value. If necessary, breathing is adjusted to ensure the desired concentration again. At altitude, the body will start breathing faster to be able to supply the body with the necessary oxygen. This faster breathing is good, because a lot of oxygen is needed to release energy to get up the mountain. However, this also causes us to lose more carbon dioxide in the exhalation; the concentration of carbon dioxide decreases in our blood. During the day, this does not cause any problems because one can consciously breathe and will not suddenly stop. During the night this becomes a bit more annoying, as there is no conscious breathing. So breathing will work purely on the basis of the concentration of these two gases.
Even during sleep, breathing speeds up in order to take in enough oxygen in the blood at the lower oxygen tension. At the same time, the carbon dioxide concentration in our blood drops below the desired level. The body therefore wants to increase the carbon dioxide concentration again and does so by stopping breathing for a while (this is called sleep apnoea). However, now the oxygen concentration will be below the desired level, because the person has stopped breathing. To replenish it, the person has to breathe faster. At this point, one sometimes wakes up restless. After falling asleep again, the same thing will happen again.
Restless sleep is therefore a normal occurrence. Apart from broken nights and not feeling rested, it will not do any harm. The medicine Acetazolamide can reduce sleep apnoea, allowing one to sleep better. It is recommended to use 250 mg per day.