If you are 6 feet tall, How do you hang from a top bunk? The top bunks are not 6 ft off the ground, they are eye level. Hmmm, something doesn't add up.
A person determined, certainly can do it.
It doesn't take long. Once the bloodflow is restricted to your brain to the point of passing out, your body relaxes, and gravity does the rest.
Lots of people have died from auto-erotic hangings that weren't trying to kill themselves, for that very reason. Most all of them just had to stand up.