Looking back on my previous habits, I was probably drinking at least one litre of Coke per day: I'd have a 500ml bottle in the morning, then another one at lunchtime, and maybe more in the evening (particularly at weekends).
I went off to visit friends on Sat 17th December, and I didn't actually drink any Coke that day. This wasn't a deliberate choice, it's just the way it worked out, but I did have two glasses of wine while I was there. When I woke up on Sunday morning, I had a bit of a headache. This didn't really feel like a hangover, and I drank water on Saturday as well. Once I drank some Coke, the headache went away, which suggests that it was just caffeine withdrawal.
After that, I considered cutting out Coke altogether. However, the following day (Monday 19th), the boss asked me to make some changes to an Excel file. This turned out to be more of a numerical analysis challenge than an IT issue, so I had to dig through my brain of cheese to remember my old Maths classes. I figured it out in the end, but I could also tell that I wasn't at peak productivity. So, for the rest of the week (including Christmas Eve) I rationed myself to one "dose" per day: either a 330ml can or a 500ml bottle.
On Sat 24th (technically Sun 25th), I went to bed at 04:00, then I got up at 13:30 (9½ hours sleep). I spent the day watching TV, then went to bed at 22:00 with a headache. It took me several hours to get to sleep (I think I was still awake at 03:00), but I was literally resting my eyes: I was more comfortable lying in the dark than keeping my eyes open in the light. My basic plan for the week was to follow the advice in Scientific American: "Go to bed when you are tired, and allow your body to wake you in the morning (no alarm clock allowed)."
On Mon 26th, I got up at 08:30 to use the loo, then went back to bed, and got up properly at 13:30. At a guess, I slept for about 10 hours altogether. This was another lazy day, still with minor headaches. I considered taking paracetamol, but I read a lifehacker article which talked about caffeine interfering with adenosine receptors in the brain. I'm not sure whether there are any similar issues for paracetamol, but I don't want to replace one dependency with another, so I just decided to put up with it. I then went to bed at 04:00, so this wasn't doing a great deal to improve my routine.
On Tue 27th I had to set my alarm (visiting family) although I slept until 10:00 which was later than intended (6 hours total). I felt ok during the day, so I thought that I was over the headache period. I had a glass of wine (my first since Sat 17th), and I then got a big headache on the bus journey home at 20:00. I made an effort to drink lots of water, since that seems to be the standard advice for dealing with headaches, and went to bed at 00:15.
On Wed 28th, I woke up at 06:00, bursting for the loo, but I still had a headache. I drank some more water and went back to bed (getting to sleep at about 07:00), then woke up again at 13:00 when I needed to use the loo again. Based on that, I don't think that lack of water was the main problem; it seems to be the combination of alcohol during caffeine withdrawal. The headaches eased off during the day, and I went to bed at 01:15, and got to sleep some time after 02:15. That's encouraging, because it means that I'd only been up for about 13 hours and it's a more reasonable time to go to bed (at least by my standards).
On Thu 29th, I woke up naturally at 09:45 (after 7½ hours of sleep), just in time to watch Sharpay's Fabulous Adventure on TV. (Like I said, I didn't want to be too ambitious this week in terms of brainpower.) No headaches, and I went to bed at 02:00.
On Fri 30th, I woke up briefly at 09:00 then went back to sleep and got up properly at 12:15 (after about 10 hours of sleep). Again, no headaches, and I went to bed at 01:30 (going to sleep at about 02:30). That's still not "early", but I'm glad that it was about the same as the previous night even though I'd had a lie-in.
On Sat 31st, I had an SJA meeting, so I had to set my alarms, and I struggled out of bed at 10:30 (after 8 hours of sleep). I had a quiet night in, since I knew that I'd have an early start on Sunday (going on duty), but I did have a glass of wine. I went to bed at 02:30, once the fireworks and loud drunk people had quietened down.
Yesterday (Sun 1st), I got up at 06:30, after about 4 hours of sleep. It was an effort to drag myself out of bed, but I felt more alert once I'd splashed some cold water on my face and got the "sleep" out of my eyes. I didn't have any headaches after the wine, which is good. I did have to resist the temptation to buy some Coke, but that was more out of habit than anything else. In the evening, I went to bed at 01:30; I could have comfortably gone to sleep earlier, but I wanted to keep reading a book.
I was out on SJA duty yesterday at the New Year's Day parade in central London, and we found a cafe on Lansdowne Row that did a full English breakfast for £5 (or £4.50 for the veggie equivalent). I didn't make a note of the name, but looking on Google I think it was La Strada. That's amazingly cheap for the Mayfair area, and it made a nice change to the ridiculous quantity of coffee shops. That price included coffee or tea (neither of which I drink), so in situations like this I normally ask for a can of Coke as a substitute, even if it costs a bit extra. I didn't want to do that here, so I went for a Tango instead. Similarly, I've been drinking a lot of Schloer at home, for the situations when I'd normally drink Coke just because I'm bored with water. In the long run I'll try to cut down on these substitutes, but they serve a useful purpose in the short term.
Today I got up at 13:15, after about 12 hours of sleep. I set two of my three alarms for about 10:00, because I wanted to go to the Avengers marathon at the Prince Charles cinema. However, that was only a provisional plan, so I'm not too bothered that I missed it; I've seen two of those films already, and I can watch the other two on DVD. Hopefully this has cleared my backlog of sleep, so I should be able to get up at a sensible time tomorrow when I go back to work. I had another glass of wine last night, and I've had no headaches today, so I think I'm past that stage now.
Technically I haven't given up caffeine altogether, because there are small amounts in chocolate. However, I'm treating that as negligible: if it doesn't show up under "nutritional information" on the packet then I'm not going to go digging on the web to look for it. Apparently it's more common in dark chocolate, so it's probably more of an issue if you go for "proper" chocolate (e.g. Green and Black's), whereas I prefer the mass-market stuff (e.g. a Bounty or Wispa). I may go back to Coke eventually, but only when I'm confident that it will be a conscious choice rather than a slip. Basically, I want to treat it the same way I treat alcohol: something that I can go without for months at a time and not even think about.