YOU haven't had much sleep and not surprisingly you're feeling cranky and miserable and you promise yourself you'll go to bed early that night.
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Well it may not be lack of sleep that causing the blues but rather the lack of quality sleep.
A new study has found that people whose sleep was frequently interrupted reported a significantly worse mood that people who slept less due to later bed times.
Researchers at the Johns Hopkins School of Medicine in Baltimore studied 62 healthy men and women for three consecutive nights. The study subjects were divided randomly into three separate groups.
One group had uninterrupted sleep each night, one group had delayed bedtimes while the third group was deliberately awakened eight times during the night.
At the end of each night the three groups were asked to assess how strongly they felt positive or negative emotions such as anger or cheerfulness.
While there were no differences in mood between the groups after the first night, those people in the interrupted sleep group experienced a 31 per cent reduction in positive mood in the second night compared to 12 per cent for the delayed sleep group and these reductions persisted after the third night.
The team believe their findings help explain why many people with chronic insomnia experience depression - it may be down to insufficient slow-wave sleep.
Lead author Professor Patrick Finan said: "Many individuals with insomnia achieve sleep in fits and starts throughout the night, and they don't have the experience of restorative sleep.
"You can imagine the hard time people with chronic sleep disorders have after repeatedly not reaching deep sleep."
The researchers found that interrupted sleep reduced not only energy levels, but also feelings of sympathy and friendliness.
