**4.2 Secondary headaches associated with sleep disorders**

Sleep-apnea-syndrome related headaches; presents with awakening headaches (headaches on awakening rather than headaches that awaken patients from sleep). These headaches start in the morning and resolve 30 min after awakening. They are bilateral frontal headaches, squeezing in character, and daily or almost daily. There is no associated photophobia, phonophobia, or nausea. These headaches are most commonly caused by obstructive sleep apnea (occur in 18–60% of patient with OSA) but also central sleep apnea and hypoventilation. Awakening headaches affects 4–6% of the general population and 18% of patients with insomnia. OSArelated headaches may also present with migraines features, chronic daily headache, or be similar to TTH [40–42]. The pathogenesis of the awakening headaches related to the OSA, is probably associated with hypercapnia, vasodilatation, elevated intracranial pressure, and poor sleep quality [43–45].

Medication overuse headaches (MOH) is also associated with sleep disorders: MOH is a secondary form of headache triggered by the frequent use of acute pain medication for management headaches. MOH is associated with poor sleep quality [2, 3, 9].
