I have IBS. IBS is a funny disease because what bothers you one day may not bother you the next. Ingesting foods and/or beverages that can trigger IBS is always a risk, particularly if the foods and beverages are combined.

Another thing with IBS is that you cannot overeat. Overeating is a trigger as is eating or drinking acidic foods / beverages. Alcoholic beverages are acidic and irritate the GI system. Sinus problems are not an issue with IBS and are caused by other factors, e.g., a cold or flu. Colds and flu (as well as IBS) can all cause diarrhea. So, in my informal diagnosis, it sounds like you might have had a combination of things.

It is a good idea to stop drinking alcohol until your GI system settles down. Then, gradually introduce it to you diet to better deduce your tolerance level. Also, be careful not just what you eat but how much. Water does not protect you from IBS symptoms. To my knowledge, it also does not dilute what you ate or drank to minimize the effect problem foods / beverages could have on your GI system. Could you let me know why you believe drinking a lot of water will minimize your IBS issues?