Why do I get hangovers seemingly at random?

I’m 19, so decently new to drinking, and I used to consider myself someone who never got hungover. That did lead me to adopt some pretty bad habits (like not drinking water before bed), which I’m trying to work on. I’m just confused as to why my hangovers seem completely arbitrary.

A couple weekends ago I way overindulged and had about 14 standard drinks in one night, which was way too much (at least for my tolerance) and I was absolutely trashed. I slept for about 4 hours and felt fine in the morning. Yesterday I had about 5 standard drinks, felt absolutely fine, and got like 6 or 7 hours of sleep. I feel like shit today and can’t keep down any food.

Yesterday I did drink before I’d had food, but I made myself some eggs after. Is an empty stomach/not drinking water really that big of a factor? Does that mean they’re entirely preventable (for now)?