Could an ambien (zolpidem) tab not activate right after ingesting? i wasn't able to fall asleep, but 8hrs later, i got dizzy with vertigo. i ate 2x in between.

Doubt it: I would doubt that it would do that after that length of time. If it dissolved too slowly, you could not notice much, if it dissolved too fast it could have made you feel funny sooner than that.

A bad generic ?: I personally have taken a generic of Ambien (zolpidem) that while it did help me sleep caused me to feel dizzy, nauseous, and to have brief spell of vertigo in the morning as well. I have had patients describe certain generics that simply did not help with sleep when the brand always did. So while I am very concerned that people take Ambien (zolpidem) the correct way, I do believe there are some bad generics out there.