I think the better quick alignment check is to focus your left eye on a fairly bright star through the binocular. Then de-focus the right eye as much as possible with the diopter adjustment. Then look through the binoculars with both eyes at the same time. If the focused star is near the middle of the defocused star you are in good shape. If the focused star is outside of the defocused star your alignment is not good. This method will probably better detect significant misalignment in the horizontal direction than the 'straight line' test.
This method, or variations of it, is pretty nifty too especially if you want to check multiple IPD settings:
5 - Nuevos artículos - Collimation of Binoculars with a Lamp, a Mirror and a Screen (recommended)
Exposure to too much light seems very unlikely. There are transmission losses through a binocular, so the amount of light reaching your retina is generally less through optics than unaided viewing (unless you are specifically looking at something very bright like the sun or a laser or a specular reflection of either).
I wouldn't discount the possibility that your eyes just don't agree with the optics of this binocular. Maybe you are getting the rolling ball effect? If you are really putting a pair of binoculars to the test and doing a lot of scanning and looking around within the FOV this could cause some eye fatigue. You can find a lot of posts on this site about people who have had trouble with specific binoculars (often binoculars with very wide and/or flat or flat-appearing fields). It could be that your eyes/brain are much more comfortable with a modest field with gentle curvature or pincushion distortion. Even the very 'best' optics can be disagreeable for some people and it is highly dependent on the individual user.
Constantly fiddling with the diopter might be a problem too. Bill Cook (WJC) posts on here about this all the time. You don't want your eye muscles and the diopter battling each other for best focus. Your eyes end up strained and you don't get a good diopter setting. Ideally your eyes will be relaxed (focused at infinity) for diopter setting.