Yes, it can cause vertigo, though I don't know about 6 days later.
The whole "safer than alcohol thing" is extremely shifty. It depends on how much alcohol (a single glass of wine a day is good for your heart and isn't enough to get most people even tipsy), whereas no one smokes weed with any intention of anything other than getting high and the effects are pretty immediate.
Pot's not the worse thing for you, but I've never met a pot head where I was surprised they smoked weed, even if they had stopped years before. That flakiness never seems to go away. It's their choice, of course, but I think people should at least recognize what the repercussions could be.