Commercial or passenger aircraft are usually designed for optimum performance at their cruise speed or VC. Combustion engines have an optimum efficiency level for fuel consumption and power output. Generally, piston engines are most efficient between idle speed and 25% short of full throttle.
The blood to your head rushes when you do a quick movement, so, naturally, dizziness is expected. I think the blood rushes from your head too fast. it is called postural hypotension.. whereby, due to getting up suddenly to a upright position, there is lower blood supply to th head.
Lightheadedness occurs when your brain does not get enough blood. 1  You have a sudden drop in blood pressure. 2  Your body does not have enough water (is dehydrated) because of vomiting, diarrhea, fever, and other conditions.  You get up too quickly after sitting or lying down (this is more common in older people).