I've been sleepy all day, so I drank four cups of coffee over the course of the day. As befits my laughable caffeine tolerance, they were decaff; four cups is over twice my average coffee intake in a working day, but it's still four cups of decaff.

All evening I have felt wired, light-headed, and jittery. I'd thought my tolerance had been on the increase recently (it had been taking me two cups of decaff to wake up in the morning rather than one!), but if four can still get me into this sort of state then I think it has a pretty long way to go yet.

Every so often I've wondered if I was just imagining my ludicrously low tolerance, and if it was just psychological. Well, it would have to be some pretty strong psychology to do this to me.

Now I just hope I can get to sleep OK…