After a couple of weekends of hard work on free software recently, I was feeling pretty tired, and decided to dedicate the weekend just past to intensive rest and catching up on my sleep.

It turns out that if I really try hard to catch up on sleep, and succeed, then I become noticeably more caffeine-sensitive. I drank the same amount of coffee yesterday as I would normally drink on a Monday morning, and it made me anxious and unhappy for most of the rest of the day, and then it took me hours and hours to go to sleep last night. So now I've completely undone all of the weekend's good work and am short of sleep again. Arrgh!

And now I think about it, I remember this same thing happening on a few other occasions too, particularly when I get back from holiday. Apparently it's a thing I ought reasonably to be able to predict and allow for. But I didn't – and I can't even use ‘being half asleep’ as an excuse…