Hey Kim -
I lost about 20-30kg and gained back about 10kg....
I originally lost the weight by making lifestyle changes (eating better, increasing the incidental exercise). I managed to maintain my loss for a year as I lived in Ireland.
I regained my weight after coming back home - I had missed FOOD - Mum's cooking, all the lovely different restaurants in Perth, and I went a bit mad! (seriously, no-one goes to Ireland for the cuisine...)
I also got back into uni and was so busy I "forgot" to exercise, and then I was forgetting to eat and having to grab from vending machines, and takeaway.. and so on.
I've recognised the problem, and I'm working on it now!
I think the MAIN reason I regained was because I got into "holiday mode" as in, I deserve a treat, I've done so well, so I'm going to have it! Which is a fair enough attitude, but maybe for a special day or week, but not for MONTHS!
My advice to you is to be careful this holiday season - have fun and let loose, but try to keep the non-party days healthy, and have a definite "end date" to the holiday fun to get back on track!
I'm sure you will do fine maintaining your weight, you have come so far!
Good luck Kim