This confusion steered Kennedy down a horrifying spiral to his death on that hot and hazy night in July. If you've ever felt the searing pain of belly-flopping off a diving board, you might rightly suspect that hitting the water at high speed is an impact not much different from colliding with a granite cliff. The kind of bafflement and panic that killed Kennedy arises in a mind as it struggles with the contradictory signals of its inner ear and its rational faculty. Reason and emotion are at war. The inner ear evolved over millennia to measure one's movement in relation to the fixed sensation of gravity.
Gravity always acts as a vector pointing straight down to the center of the earth.
The inner ear is equipped with tubes of liquid that shift in response to any movement while the mind compares these signals against this fixed sensation of gravity. The airplane's flight path creates forces that befuddle one's awareness of earth's gravity. To judge by the sensations in the seat of your pants, you literally can't tell up from down, left from right. You are as helpless to move out of the airplane's acceleration field as you would be if you were pinned to the side of a spinning circus centrifuge when the floor drops away. I take Saint-Exupery's sentiment about the heart's efficacy to mean that emotion is the proper tool for grasping what is essential about life.