I never had this problem until one day when i was squatting.  I think it was 4 plates but i was coming off a little layoff.  I did my set, stopped, laid on the floor like usual, but the dizziness never left me.  I had blacked out once before so i knew the feeling.  I went up to the reception desk and told the girl i felt faint and she took care of me.  
Nowadays an intense set of BB curls makes me fucking dizzy.