Assuming you are doing the right thing, and optimizing your form for water entry, you will simultaneously be minimizing your wind resistance during the fall: 1.) A fall from 30 feet will result in a velocity of roughly 44 ft/s = 30 mph.2.) A fall from 100 feet will result in a velocity of roughly 80 ft/s = 54 mph..) A fall from 150 feet will result in a velocity of roughly 97 ft/s = 66 mph. 4.) A fall from 250 feet will result in a velocity of roughly 125 ft/s = 85 mph. The first case is a tower jump I did for the Navy, and is trival for anyone who is HWP and doesn't belly flop.
Fainting spells or feeling faint is caused by not enough oxygen getting to your brain. Passing out for a very brief period, coupled with a quick recovery, is medically termed syncope. And having a syncope moment will suddenly happen at some point in the lives of about a third of the population.
Well, you can guess that there is a better medical term than passing out, and you'd be correct. A temporary loss of consciousness is referred to as syncope. And it happens when there is a sudden lapse of blood flow to the brain. Your brain doesn't get the blood it needs, and - WHAP! - you've fallen on the floor. Syncope can happen to anyone. A late 90s study showed that as many as 20% of people can experience syncope.