That's active 3D. Active 3D is the type that needs special glasses (each costing roughly £40 a pair) which will melt your brain after a while.
You want to go for Passive 3D technology, that's the same type used in most cinemas and you can even use the same glasses. It's much better on the eyes.
I've got a 42" 3D Samsung one that is fantastic, came to about £600 and i've also got an AOC 23" 3D PC Monitor that came to around £120. Both use Passive 3D technology and I never get headaches from them, although, that can always depend on the person.
We have Active 3D, which I am only allowed to watch rarely (dad's decision). You can switch 3D on and off by pressing a button on the remote and going back to the normal HD like you said, mangoh. I haven't experienced headaches or pain in my eyes whilst watching it, but I have only watched it a couple of times, besides it's your choice
@AndyKelly Thank you and I'll keep it in mind but as I mentioned before I rarely watch Active 3D anyway.