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.
Low blood pressure when you stand up. Fainting can also be caused by a fall in blood pressure when you stand up. This is called orthostatic hypotension, and tends to affect older people, particularly those aged over 65. It's a common cause of falls in older people.