Here is something I learned when I started having serious nasal congestion associated with seasonal allergies. Alcohol will absolutely make it worse.

I've never had congestion caused by alcohol, but it definitely made mine much worse. So I don't drink in the Spring, on days when the pollen is high. Alcohol causes the little blood vessels inside of your nose to expand. Basically, that's what nasal congestion is. People tend to think that nasal congestion is due to having a lot of mucus up in there. That's really not true. When you can't breath through your nose, it's because the lining of your nose is swollen due to enlarged tiny blood vessels in that lining of the nose. Alcohol can definitely make that worse.

Usually, though, that effect would be felt soon after drinking, not the next morning.

Also, alcohol is an irritant to the mucous lining of your stomach and gut. That's why heavy drinkers of straight booze often end up with gasto-intestinal bleeding. Even just one night of heavy drinking can certainly cause diarrhea. Most people with any significant experience with alcohol are familiar with the nausea that can go with drinking.

For one or two drinks to cause the trouble you describe is not typical, but I believe it would be possible. Basically, you are the best judge of that. Also, not every one means the same thing by one drink. More than 6 ounces of wine in the glass is more than "one" drink.

As far as hangover symptoms go (which I've experienced plenty of when I was younger): Keeping hydrated will supposedly minimize headaches. It's sure not going to reduce vomiting. Anything you add to the volume of stuff in your stomach will just aggravate vomiting. I notice you said you were vomiting up water.

Certainly, people do vary a lot in their tolerance for alcohol. Some of that is due to genetics. Some of that is due to experience. Flushing in response to modest alcohol intake is generally due to genetics. (It has to do with dilating those little blood vessels in the skin.) Generally, alcohol dilates peripheral blood vessels - like in the nose and in the skin. That's why people feel warmed up when they drink.