A grey out is a perceived fading of light and color, accompanied by a loss of peripheral vision (tunneling.)
It is a precursor to fainting or a blackout and is caused by hypoxia (low brain oxygen level,) often due to
a loss of blood pressure. A grey-out may be experienced by anyone experiencing high positive g-forces forcing
blood to the lower extremities of the body and lowering blood pressure in the brain. Continued, or heavy g-force
will rapidly progress to g-LOC (g-force induced Loss Of Consciousness.)