To use this trick, you need to make your character vomit. This works best by eating a common bulrush, which will induce vomiting immediately after.

Now how does this tie into surviving great falls? The answer is that the vomiting animation stops you from going into ragdoll mode and therefor can negate any fall damage. So if you want to get down a mountain or cliff quickly that would usually be deadly, follow these steps:

1) Go to a cliff / mountain / wall /whatever
2) Step on the edge so that the left side of your body is positioned right at the edge.
3) Eat a piece of common bulrush
4) At the beginning of the vomiting animation, your character takes a step to the left, thus making you fall down if you positioned yourself correctly.
5) Laugh during the hilarious vomit induced fall
6) Arrive safely and unharmed on the ground
7) Continue your journey.