Blood shot eye?

The reason why your friend eye is getting red because when he drinks that raises the Blood Pressure Level, when he is sober, the level will decrease. Also there are tiny veins in your eyes, and when you drink it puts a strain on your eyes and causes these veins to swell, sometimes it has been proven that some of them can burst. So my advice would be to tell your friend if he/she has an alcohol problem to not drink as much, not until they are fully drunk anyways.

You could have pink-eye. That can spread to the other if gone untreated. At least rinse the eye with water for 20 minutes, letting the water drain away from your face. Next level would be eye drops such a Visine. Next is having a Dr. examine the eye. Good luck Response to your edit: 4 1/2 hours is not enough sleep. You need at least 6. 7 is the perfect amount for me.

Sorry to say the only thing i can come up with is your blood vessels may constrict a bit more than the other one.