Low blood oxygen levels (hypoxia) and high blood carbon dioxide levels (hypercapnia) can cause headache due to issues with oxygen circulation in the body. This can develop when travelling to high altitudes, aeroplane travel, deep sea diving, and sleep apnoea. Headaches manifest differently in each situation due to differences in pressure and oxygen deprivation. Altitude headache caused by mountain climbing generally affect the entire head, are mild to moderate, and are exacerbated by exercise; whereas headaches from aeroplane travel are at the front of one half of the head with a severe stabbing quality. Diving headaches are usually accompanied by symptoms of carbon dioxide intoxication, such as confusion, light-headedness, incoordination, laboured breathing, and facial flushing. Sleep apnoea headaches occur on waking in the morning, and are usually chronic (occurring on more than 15 days a month).
Hypnic Headache – this is another headache type that is related to sleep. Sleep apnoea can be dangerous in some cases, so it is important to differentiate between hypnic headache and sleep apnoea.