Headache caused by hypoxia and/or hypercapnia and occurring in conditions of exposure to one or both.
A. Any headache fulfilling criterion C
B. Exposure to conditions of hypoxia and/or hypercapnia
C. Evidence of causation demonstrated by at least one of the following:
1. headache has developed in temporal relation to the exposure
2. either or both of the following:
a) headache has significantly worsened in parallel with increasing exposure to hypoxia and/or hypercapnia
b) headache has significantly improved in parallel with improvement in hypoxia and/or hypercapnia
D. Not better accounted for by another ICHD-3 diagnosis.