I think mentally you "feel" as if you have more testosterone because of increased confidence and esteem. I know what you mean though because when I was smack dab in the middle of 3 years of training, I was freakin pumped, aggressive, and horny as hell. Didnt take any gear either. Though after 2 years off because of an injury, I have no where near the aggression, or sex drive. I personally think it has alot to do mentally. Goes with saying "you feel as good as you look." Just my .02$. Though I would like to see some documentation to support the raise in test with increase of muscle mass.