after i heard about garlic possibly being bad for the brain, i stopped eating garlic for about a month. then one day, to experiment, i made my usual stir-fry with the usual amount of garlic i used before. the best way i can describe what i felt is "tryptophan overdose". my head felt heavy and all i could do was go to sleep. i'd no way drive feeling the way i did. i felt this probably 30 minutes to an hour after eating. i felt pretty horrible and mostly stopped eating garlic since. i used between 4-6 cloves for an amout of food that could feed 3-4 people.
on a similar note, before i ever knew about how onions are related to garlic, over the years i started getting headaches from eating burritos. i never knew what caused it so i just stopped eating them. well, one day it dawned on me that maybe it was the onions. so i ordered one without the onions and have never had a headache from burritos since. so from my experience there is definately something about garlic and onions that affected my head and awareness.