No! Move you idiot!

Nightmare spotting a bone dagger hurling towards you during a battle with the Star Sanses sends Nightmare in a panic. That bone dagger will kill you if it hits you and Nightmare is fully aware of this. He acts on instinct and shoves you out of the way just before it could hit you. Now Nightmare has a bone dagger lodged in his back. He grits his teeth and endures the pain. You're safe and that's all he cares about.