"When your sleep is disrupted throughout the night, you do not have the opportunity to progress through the sleep stages to get the amount of slow-wave sleep that is key to the feeling of restoration," said study lead author Patrick Finan from Johns Hopkins University School of Medicine.
The researchers studied 62 healthy men and women randomly subjected to three sleep experimental conditions -- three consecutive nights of either forced awakenings, delayed bedtimes or uninterrupted sleep.
Participants subjected to eight forced awakenings and those with delayed bedtimes showed similar low positive mood and high negative mood after the first night, as measured by a standard mood assessment questionnaire administered before bedtimes.
They were asked to rate how strongly they felt a variety of positive and negative emotions, such as cheerfulness or anger.
The researchers said significant differences emerged after the second night. The forced awakening group had a reduction of 31 per cent in positive mood, while the delayed bedtime group had a decline of 12 per cent compared to the first day.
Researchers did not find significant differences in negative mood between the two groups on any of the three days, which suggests that sleep fragmentation is especially detrimental to positive mood.
Many individuals with insomnia achieve sleep in fits and starts throughout the night, and they do not have the experience of restorative sleep, Finan said.
The study appeared in the journal Sleep.
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