Millions of people wear digital sleep trackers to bed every night, waking to see the pattern of their slumber. But, to date, the understanding of these night graphs is relatively simplistic. It’s easy enough to tell how long a person spends in various modes of rest and how often they wake up. But the bigger picture, how individual nights and even weeks of sleep tie together, remains an open question, one that a team of researchers at UC San Diego, working with colleagues at UC San Francisco and the City University of New York, is beginning to explore by analysing millions of nights of sleep ac…