The Advance-Wars-Before-Bed-Guaranteed-Headache Effect

I don't know why it is this effect persists, and I wonder. I've played this game a lot through the years (closing in on a thousand hours with the DS one now), and I don't recall ever getting headaches quite this often... they vary in severity, but every single time I play Advance Wars before I go to bed now, I know I'll wake up with a headache the next morning.

I'm starting to wonder if it's a self-fulfilling prophecy - so called placebo. Or if there actually is some element to the game that science might prove causes this.

Is it just the blue light? Switching off hastily right before you try to sleep?

Is it certain animation and movement?

Is it simply the device, that burdens the eyes? The small screen?

Is it the way I play - how I hold the console? That my neck tenses up when I do? That I elevate my head in a strange position as I play in bed?

Is it tension? Do I go into the wars with such a sense of immersion that they leave me with this kind of effect after?

Is it the late hours - that I just don't get a proper amount of sleep when I do? Are any of these other effects amplified by the night, and lack of surrounding light?

Is it temporary dehydration? Do I need to drink more water when I play games that sometimes last an abundant amount of time - though I always drink a glass right before I go to sleep after?

If it's any of the above it seems likely it comes down to simply the device + how I play it. Some combination thereof. Some day I'll try sitting upright and playing it in a more comfortable pose, but I don't think it'll make THAT big a difference.

Fortunately these are headaches that for the most part fade away relatively quickly as soon as I get up... but sometimes they don't, like today, when we're having guests over in a few hours.

Might have to resort to painkillers hmm. We'll see. First step coffee.

UPD: It did fade away after all. :)