This really has nothing to do with the 3DS, since the 3D is turn off-able. But I know some people who get headaches when they go to 3D movies at the theaters. Hank Green of the vlogbrothers has had a hand in inventing 2D glasses!

YouTube - 2D Glasses! Take the Headache out of 3D

I thought it was really cool how he came about it. And sweet.

Here's the site if you want to check it out.

2D Glasses

Oh yeah, I saw those. They're pretty awesome, even though they don't block out the 3DS 3D.