Superfly, are you referring to the power curve or as per the op, the drag curve?
If referring to the drag curve, an aircraft is on the "wrong" side of the drag curve when it is operating below its minimum drag speed.
When operating above minimum drag speed, if the aircraft is upset (say a gust) such that the speed increases, so too does the drag. Without touching power, the increase in drag will then slow the aircraft back to its original speed. Likewise, if the gust results in a reduction of speed, the drag reduces which then allows the aircraft to accelerate back to its original speed without touching the power. This is a "stable" condition, i.e. an upset results in a return to the original state.
When below minimum drag speed, if the gust results in a reduction of speed, the drag increases (increased angle of attack to stay level) which slows the aircraft even more, resulting in more drag, which slows it even more... etc. At some point, an aircraft may subsequently run out of power to be able to accelerate the aircraft back to a suitable speed.
Looking at the Concorde crash, seeing it struggling along at a high angle of attack and knowing that its on the wrong side of the drag curve, with no more thrust available to accelerate, and no altitude to use to accelerate, you know that there can only be one result...(systems failures aside).
An application of the drag curve is the holding speed for a jet. Maximum endurance normally occurs at the minimum drag speed. If a jet was in the holding pattern at exactly minimum drag speed, when it rolls into the reversal turn where the drag increases, without touching power the aircraft would slow to below minimum drag speed where it becomes speed unstable. Consequently, jets tend to hold at a speed just above minimum drag speed so when the drag increase in the turn slows them down, they are still above minimum drag speed when they roll out and increase speed back to their original holding speed without needing to touch the power.
There is not normally any control reversal associated with being on the wrong side of the drag curve.
Hope this helps.