Walked up to mob to attack it, and got thrown several meters into the opposite direction

What I expected to happen was...:
I was expecting to attack the mob and to kill it.

What actually happened was...:
Ocassionally in survival, I would go to attack the mob and it threw me in the opposite direction several meters.

Steps to Reproduce:
1. Walk up to mob, touching it's hitbox with the player's hitbox
2. In survival, the player will be hit (just walking up to it) and thrown several meters, depending on how high off the ground the player is standing.