Your body keeps a ledger of every hour of sleep you borrowed and never repaid.

Sleep debt does not announce itself as tiredness. It shows up as a short temper with your spouse, a careless mistake in a report you checked three times, a craving for sugar at four in the afternoon.

You cannot repay it all on Saturday. The body settles in instalments: twenty extra minutes a night, the phone charging in another room, the last message answered before eleven.

This is not indulgence. Sleep is when the mind files what you learned and the body repairs what the day spent. Skip it long enough and you pay in judgement, which is the expensive one.