Ok, bear with me as I try to explain this bug:

Make a wall with some lava on it flowing down. Throw and Ender Pearl at the lava and quickly save and quit before it hits the wall.

Now load the world again and DO NOT DO ANYTHING ELSE (even moving will cause this to not work!)

The ender pearl will teleport you into the lava, and it will take a few seconds for you to start taking damage.

You can look around with the mouse, but pressing WASD (or arrow keys) makes the effect go away.