Motion induced Blindness
 

I'm not sure if this should be here or in medical matters but here's an interesting site that was posted on the PFA bulletin board Motion induced blindness

this is quoted as the Reference source

Ohhh, my eyes are watering! :ooh:

Not feeling too well on one particular day, i had a student practising steep turns.
Only 2g started to get tunnel vision, just like looking down a piece of tube, very strange.
Never experienced before or since but could feel myself heading towards a blackout.

Goes to prove, if you don't feel well, don't fly.