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.
Standing Up too Quickly. When a person changes position suddenly, such as from a reclining or sitting position to standing up, the blood in the head is pulled by gravity into the feet and legs. This abrupt change in blood flow can make the person's blood pressure fall briefly before the body has time to counteract it.