A new study has surveyed 17 astronauts to see what sort of headaches they experienced while on space missions. Headaches were much more frequent than on earth and didn’t fit a known type, suggesting that zero or micro gravity may be a specific trigger for a pounding head.
Below is the part of the article where the researchers discuss how the weightless conditions of space might affect the brain to cause the headache.
To describe headache, most astronauts used terms such as ‘exploding’ and/or ‘a heavy feeling’, confirming previous observations and suggesting a change in intracranial pressure. This is compatible with headache attributed to disorders of homeostasis, which can change during a state of microgravity. Certain haemodynamic [blood flow] changes might explain the occurrence of space headache. Alteration of cerebral blood flow and volume have been shown during exposure to microgravity.
The most striking change is the cephalad fluid shift, when body fluid redistributes and the blood volume in the upper body increases. The fluid shift towards the brain and probable brain oedema [swelling] could lead to an increase in intracranial pressure. Insofar as microgravity is also known to induce hypoxia [reduced oxygen supply to brain tissue], it also might be considered as a plausible trigger for space headache