I'm sure that everyone has heard at least once that falling into water can be just as bad as landing on concrete if you are going fast enough. However most of the time, it wouldn't be the impact that would kill you. More likely than not, it will break your fall and save your life just to take it away. This is because at a reasonably dangerous height, quite a few people knock themselves out due to smashing their faces into their knees. Additionally if your body isn't perfectly positioned, hitting the water at these speeds could cause compression fractures, as well as spinal injuries. These would in turn raise your chances of drowning. The alternative would be to somehow perform a perfect dive which would also worsen your situation as you would end up deeper. There would also be the sudden change in pressure. In conclusion, if you fail your landing, you're dead and if you somehow land it, you might just panick and drown.
Now if you're falling from a plane without a parachute, you're chances of surviving are almost nonexistent. Nevertheless you should search for anything that seems breakable. It also has to be big enough to cushion your fall. A pillow just won't cut it so search for something like a tree or maybe an RV. Spread your body as far as possible to increase the area that would be affected by air resistance. This will slightly slow your fall and increase your survival chances (it will also give you more control of the situation and time to think).
Now here are just some general tips for when you fall from anything regardless of height.
Grab onto anything you can and try to protect your head. Everything else can be replaced or sacrificed. Don't tense your body right before impact as that would just cause a negative impact on your chances of survival.
If you want to survive and don't mind being disabled or the pain, you should try to orient your body so that you don't land on your head. Then just close your eyes and relax your body for impact. If you've already given up, just orient your head down to save yourself from the pain. The easiest method would be crossing your arms and spreading your legs as this would create drag from the lower part of your body.
Most likely, if you truly do fall from somewhere high, either your survival instincts or fear will take control of your body (but the fear might make you pass out which would be a good thing in some cases). At that point you wouldn't be capable of relaxing your body. But all that is just theoretical as I haven't been in such a situation yet.
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