There are times when you start the game, and instead of spawning in where you left off, you spawn high above the world spawn, so high that Feather Falling IV boots and Protection IV armor won't save you, and you plummet to your death. This has happened to me in two different realms and in my non-realm world twice in a row, so it's not limited to realms only. In realms it has happened to several different people over a few different realms I play on.

After plummeting to your death, most of the time you respawn back at the bed where you had your respawn point set. However, this last time it happened (in a realm this time), I kept dying over and over again at world spawn, not from plummeting again, but simply dying at the spot where I had landed on the ground with a gear-scattering splat, and the loop kept repeating until I exited to the main menu and restarted, at which point I ended up back beside my bed at my spawn point.