The primary aim of the present study was to estimate the incidence per annum of acute insomnia and to what extent those that develop acute insomnia recover good sleep or develop chronic insomnia. Unlike prior studies, a dense-sampling approach was used here (i.e. daily diaries) and this allowed for a more precise detection of acute insomnia and the follow-on states (the transitions to either recovery or chronic insomnia).
Good sleeper subjects (n = 1,248; 67% female) that were at least 35 years old participated in this prospective study on the natural history of insomnia. Subjects were recruited nationwide and completed online assessments for 1 year. The online measures consisted primarily of daily sleep diaries, as well as weekly/bi-weekly and monthly measures of sleep, stress, and psychological and physical health.
The 1-year incidence rate of acute insomnia was 27.0% (n = 337). The incidence rate of chronic insomnia was 1.8% (n = 23). Of those that developed acute insomnia, 72.4% (n = 244) went on to recover good sleep. 19.3% (n = 65) of the acute insomnia sample continued to experience persistent poor sleep, but did not meet criteria for chronic insomnia.
The incidence rate of acute insomnia (3 or more nights a week for between 2 and 12 weeks) is remarkably high. This said, most incident cases resolve within a few days to weeks. Incident chronic insomnia only occurs in about 2 in 100 individuals.