The first week of summer. What the circadian reset actually feels like.

The first week of summer holiday produces a predictable pattern in my clinic. Parents bring children who are sleeping late, reluctant to be active in the mornings, and irritable in ways that seem inconsistent with the freedom the holiday should be producing. The question is: what's wrong?

Nothing is wrong. This is the circadian reset. The school year imposes an external social clock on the child's biological clock — a fixed wake time, a fixed departure time, a fixed structure of alertness and activity. When that external clock disappears, the biological clock begins to drift toward its natural position. For most children, the natural position is about ninety minutes later than the school-year position. For adolescents, it can be three to four hours later. The first week of summer is the week the biological clock is finding its way home.

The drift produces the irritability. The child whose biological clock says 'seven in the morning' but whose social clock says 'you should be cheerful because it's the holidays' is experiencing a genuine mismatch. The irritability is the mismatch. It is not the holiday failing. It is the biology arriving.

The drift produces the irritability. The child whose biological clock says 'seven in the morning' but whose social clock says 'you should be cheerful because it's the holidays' is experiencing a genuine mismatch. The irritability is the mismatch.