I’ve found that when I get a hangover, putting pressure on my eyes (rubbing them when I’m in the shower, for example) really hurts. Why is this? Are my retinas dehydrated or something?
A partial answer; hangover is mostly dehydration. The oxidation of alcohol in the body consumes a lot of water, so you end up with a shortage. However, I have no answer about your eye sensitivity during hangover.
The membranes surrounding your brain, the meninges, also extend along the optic nerve to the eyeball. When you’re hung over or headachy, these membranes may be a little inflamed. At least that’s what my brother the eye doctor told me.