"It happens 365 days a year, including Christmas Day. I tend to get up and make a cup of cocoa, or I might watch Sky News. I try to avoid doing school work, but at the times when I'm as wide awake at 5am as I was at 3am, I'll go and sit at the computer and get to work.
"It's like my own shift system to accommodate my insomnia. My wife's got used to it, or so she tells me."
Charles, head of a medium-sized Birmingham comprehensive for the past two years, has had difficulty getting to sleep all his adult life. But his problem grew far worse when he became deputy head 11 years ago.
"As deputy or head there are always problems and challenges," he says. "For the last few days - and nights - I've been focusing on an open evening. On other nights I've found myself designing classrooms."
A long-term back problem increases his difficulty in getting to sleep, as does his rhinitis, or perpetually blocked nose. And medication has not worked; a course of homeopathic medicine left Charles drowsy in the mornings.
Instead he keeps late-evening activity as low-key as possible, with lights dimmed and sound levels at a minimum; but it doesn't stop him waking up. The resulting tiredness can be embarrassing.
"In teaching you need to be absolutely on the job," he says. "A girl here has just banged her head during school time - we could find ourselves on the front page of the evening newspaper. I have to stay alert.
"But after bad nights I have found myself overly sleepy at public events, and at meetings with senior figures in education. At other times I'm light-headed and make daft, flippant comments."
But Charles soldiers on, regardless of the exhaustion, and continues relishing his job.
"I believe it's a very lucky person who doesn't have trouble sleeping when in a responsible position," he says. "I dread the clocks going back, because it means I've got an extra hour to kill, but I take insomnia as a way of life - and can even see the advantages. If I've got paperwork to do I sometimes use up the whole night instead of a whole school day."
Charles Alexander is a pseudonym