hmm, I read all this... you just made me think and I must agree whenever i was dehydrated I felt dizzy and weak as well. It definitely didn't go away quickly. I'm not a doctor but I thought there could be perhaps a mild form of dehydration, maybe these could be telling symptoms.
The truth is, it does last for a very short moment, just when I'm about to contact the ball. Maybe the eye adaptation could take a little time, as someone suggested. I only very recently started wearing reading glasses but I also have this issue for quite some time. Strange thing is, it doesn't always happen but it will surprise me at the worst possible moment, when I least expect it.
BTW: My apology, I think this should've been in health section.