Two chaps in our airline have had this viral condition over the past twelve months. One is now back at work - the other will be shortly. Obviously knowing which way is up is important in our line of work so the CAA were very thorough in ensuring they were 'cured'.
Basically, as I understand it, the virus causes a thickening of the fluids in the innere ear which prevent the balance system from working - sending false signals to the brain - like having a spirit level bubble suspended in treacle is how it was explained to me.
Suggest you look at a medical website for an exact description of the condition. Try:
Web MD
Suffering from it certainly will cause a loss of medical certificate - for more than six months in the case of the two blokes I know.
Good Luck
[ 16 November 2001: Message edited by: Capt. Horrendous ]