Crashed after death and lag when killing

I started a new map to test all the new 1.9 things. I tried to kill some animals and the knockback i gave them was reeaally slow. It was like they were floating for a short while. Not sure if that's normal but i guess not. Then i went on to test the wingsuit thingy from the end. After hitting the ground too hard in survival I died and Minecraft froze and i couldn't do anything else not even switch to my desktop or other programs I had opened. Please help