Just how many depends on where you get your information from, but a percentage of 3DS gamers struggle with tiredness and headaches as a result of playing the 3DS.
So naturally third parties are scrambling up solutions. One is GamingZap, who has come up with the 3DS Hed Saver (yes, they did seem to forget an 'a' when naming the product).
This is a special cooling pack that works straight out of the box to keep you refreshed and headache-free.
It has also been designed for playing on the go, with GamingZap claiming the product fits comfortably in most 3DS cases. So no more having to stop playing on the train!
Mind you, there doesn't seem to be any scientific reason this would work, with the Website being light on specifics, so take this news with a pinch of salt.