h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

There is of course a simple solution for handling these excesses: TRAINING.
If one only parties at the end of the year, it is simply not enough. One doesn't run a marathon without training either.

I tried this form of training, and it seemed to work. My alcoholic threshhold was much higher and,of course, through this so was my ability to party. Unfortunately, when you take a break from the festivities and parties and have a period of rest afterwards, all the virus's and bacteria can get through your depleted defences. So now I'm ILL with some flue-like lurgy and the training has definitely stopped!

I feel sorry for you, but you could try to change the "training-schedule": there's more to partying than just alcohol (and other drugs).
Personally, I seem to have found the right balance: my body knows how far I can go without suffering afterwards, and most of the time I don't even have to go that far to have a really good time.
So, I just "listen" to my body... It's

I listen to my body...at the moment it's going gurgle, gurgle, thump, thump, woosh, woosh. A bit like a gin&tonic being drunk, in fact...and I haven't touched a drop.

Obviously, your body is right! You'll just have to find out about WHAT exactly...

Dear Doctor, you'll be glad to know that I'm feeling a lot better now and I've started running again ready for the new fell season. I'm a totally reformed character. You were right all along and now I listen to my body. When it says fill me with cider, then that's what I'll do. Strangely, though, it seems to say it all the time!! Only joking.. No really, I'm reformed now.

I'm very happy to hear that.
Keep up the good work (running and filling your body with cider), and remember who's the boss. (You can't let those bodies have their way all the time either.)