At low concentrations, alcohol can have a stimulant type effect. as the bac rises above .06, the drinker may begin to experience a "down" feeling. what is this effect called?

Every time alcohol is presented into the system, the biphasic effect, or “biphasic curve,” follows.  The biphasic is a two phase effect: first, the body experiences an energizing, perhaps “positive,” component and second followed by the introduction of the depressant, “negative,” effects of alcohol.  There is a point at which one can minimize the undesirable consequences associated with drinking. In other words, drinking beyond this point will outcome in enlarged negative consequences. This means for college students, that students who currently drink at or below this point of diminishing returns should stay at this point if they haven’t had problems associated with drinking.  Those who are drinking further than this point should reflect reducing their intake to maximize their returns. Most significantly, everyone has to find his own limit grounded on what he wants to get out of drinking. 

The answer is observations and interpreting.

It's cell theory. easy name i would think.