Garlic is incredibly powerful, even stronger than a number of Antibiotics . It is, at least in its raw form. An experiment was done way back by a former regular here (North) showing this to be the case.
I'm not sure how potent cooked garlic is. I know that the potency is diminished when garlic is cooked or roasted, but there is still some effect left. So yes, you can easily get die-off from garlic, but I'm not sure how much from cooked garlic.
Also, an important thing to remember about garlic is that it does kill both bad AND GOOD intestinal flora, so one can experience a lack of energy from depletion of good intestinal flora. This should not be confused with die-off. Everyone who is eating large quantities of garlic needs to be taking good probiotics at the same time.