I always took it in the morning. If your feeling dizzy, that'd probably be the best time. Did the doctor tell you a time? If not, thats the time I would. If you take it at night you'll hopefully be able to sleep through the dizzies. However, as I'm sure you know, Pills work like this
/ --- _____ See, It builds up quickly, and then drops off quickly. Well, that slo means that also means that if you take it at night, you're sleeping for the time when its at its most effective. Once its has built up effective plasma levels, that isn't as important, but now it sort of is. I would still say sleep though it or at least find something else you can take to alleviate the vertigo. I'd talk to your doctor about that. S/he can probably suggest something.