It could be a form motion sickness. Not all motion sickness presents as nausea.

Some symptoms include confusion, headache, diarrhea and fever.

NASA also mentions "the space stupids", something experienced by both astronauts, pilots and commercial airplance passengers which is a mild form of confusion and slow response generally brought on by fluctuating g's (turbulence, speed changes) and slightly off pressure settings.

Some physiolgists suspect that the near 0 humidity causes a feeling of dryness in the nasal passages which then fools the brain into initiating a histimine response. In otherwords, your brain suddenly thinks you have a cold and starts up a fever (remember, fevers are not part of the disease, but a defense response to a disease)

I sometimes get this too, but only in flashes and it does not last.