Is it after a certain number of awakenings? (sleeplady.com)
Actigraphy has been specifically validated with both insomniac populations and circadian rhythm disorders, and has been found to have concurrent validity with polysomnography (standard sleep study) for number of awakenings after sleep onset, amount of wake time after sleep onset, sleep efficiency, and total sleep time. (southeastpsych.com)
At night, the number of awakenings will have reduced to probably once or twice. (kaboutjie.com)