Why is my Minecraft world spawning me in the air?

This is a 1.8 Bug.

I found a forum on this, it seems to be quite common.

Until 1.9 is released, the death effects of the bug can be remedied by using slime blocks at spawn or by using a totem of undying. Obviously the former is cheaper and more desirable, but if you plan a trek to the End, always save and quit with a totem equipped.
_{^{- Spawning in midair - Mojang Bugs}}

So it seems like this is a Bug that wont be resolved until whenever 1.9 is released. So the only available solution (at the moment) is make something to break your fall.