Accidental Immortality

So, I was derping around my FTB world earlier today when I decided to take the quick route back to spawn. Going for the fastest option, I jumped off of the nearest tree. Dissapointed that I was still alive, I climbed back to the top of the tree...only to realize my health was completely full. I jumped again, and within seconds I was back to full again. Later, I discovered that my hunger wasn't dropping at all either, no matter what I did.
Did I hit the wrong key in the wrong menu, or is this a...

Accidental Immortality