How to deactivate the 3D function?

A while ago, my bf's 3DS fell from the bedside table. As a result, it started activating the 3D function by itself. Initially, it was possible to deactivate it, by making some hard movements, of by gently hitting the console with your hand. More recently, however, it's almost impossible to deactivate it, and it reactivates shortly after being shut down.

The thing is: nor I nor my boyfriend can stand to play with that damned 3D. It gives me headache, and I usually feel like it would destroy my eyes. Is it possible to kill the 3D?