Me and my friend were playing on my Creative Superflat server, and we decided to see how long it would take to fall from 100,000 blocks in Survival. As Operators, we both switched to Survival and teleported to x-y-z coordinates 0 100000 0.

What I expected to happen was...:
Obviously, I expected to go splat.

What actually happened was...:
I hit the ground, there was a hurt sound effect, and I got "

hit the ground too hard", but I was alive and not prompted to respawn. The same happened to my friend, but on my screen, my friend was floating half a block off the ground doing nothing, and on my friend's screen, I was floating in the void. When we both disconnected and returned, this was fixed, but we were still invincible to everything. The /kill command did not work, and falling in the void just assaulted our ears with pain sounds. At one point, I stood in fire, with no hunger bars, drinking poison in Hard mode while my friend hit me with a sword, and I did not die at all.
Also, we were able to reverse it by repeating the process of falling 100000 blocks. It also seems possible to complete the process faster by falling a while, then teleporting to a Y-coordinate of 3000, however this doesn't always work for me.

Steps to Reproduce:
1. Teleport to a Y-coordinate of 100000 or more
2. Change to survival mode
3. Fall until you hit the ground
4. Disconnect and return
5. You will become impervious to all damage possible in the game in any way.