Yeah, I'll give it a shot. There is a speed -- without going into a lot of math or aerodynamics -- at which an aircraft flies most efficiently. If you fly faster than that, it takes more power to overcome parasite drag. If you fly slower than that, it takes more power to overcome induced drag. Slower -- behind the power curve -- takes more and more power, because the wing (or rotor) becomes less and less efficient at producing lift, and requires more and more power to maintain altitude. (A fixed wing aircraft, if slowed down just a little more, will stall. A rotary wing aircraft, will just settle faster and faster.) You fix this problem by increasing airspeed, but since you're already at full throttle, you can't do it by adding power. The only thing left is to nose over and trade altitude for airspeed. This is no problem unless it occurs with little or no altitude to trade. This is known as running out of altitude, airspeed, ideas, and experience at the same time, and has been known to smart just a little.
Dr. Rob