First I have to say that I haven't had alcohol in ages (counteracts with my medications). I do know that it contains a great deal of calories (and is metabolized immediately in your system as sugar...explaining why diabetics should be careful with alcohol) and that it also dehydrates you. My best guess (definitely all that it is, a guess) is that the morning after ingesting the wine when you were down 2.5 pounds is that you were dehydrated and will go back to the normal weight after rehydrating yourself.
Alcohol can trick you. It has calories so must be taken into account in your daily caloric counts but it does dehydrate you. Providing you don't drink alcohol the next day you will rehydrate and be back where you should be providing you didn't immensely go over your calorie intake. I just count it as it is since I weigh in daily.