The study - the first to examine insomnia and persecutory thoughts - found that in the general population individuals with insomnia were five times more likely to have high levels of paranoid thinking than people who were sleeping well. In an extension of the research, over half the individuals attending psychiatric services for severe paranoia were found to have clinical insomnia.

The study was carried out by Dr Daniel Freeman, a Wellcome Trust Research Career Development Fellow at the Institute of Psychiatry, King's College London, who has also written about the new science of suspiciousness in a new book, 'Paranoia: The 21st-century fear'.

Insomnia has long been known to be very common. According to epidemiological surveys, on any given night one in three people will have difficulties getting to or staying asleep. For one in ten people this will occur several nights a week. Lack of sleep can lead to anxiety, sadness and irritability, but this new study highlights another potential consequence: feeling that others are deliberately trying to harm us.

"As most of us know, a few nights of poor sleep can make us feel stressed, muddled in our thinking and disconnected from the world," says Dr Freeman. "These are ideal conditions for paranoid fears to take hold. Regular, good-quality sleep is important to our psychological wellbeing."

Although the study shows a clear link between the two conditions, it is unclear which causes the other. Clinical experience indicates that there is a vicious cycle: insomnia makes us anxious and fearful, and these feelings make it harder for us to sleep.

Dr Freeman believes that the research points to a potential treatment for helping to reduce the risk of developing persecutory thoughts.

"The good news is that there are several tried-and-tested ways to overcome insomnia," he says. "In particular, cognitive behavioural therapy (CBT) has proven benefits. The intriguing implication of the research is that use of the sleep techniques may also make us feel safer and less mistrustful during the day. A good night’s sleep may simply make us view the world in a much more positive light.”

The themes of insomnia and paranoia feature strongly in the play 'Macbeth'. As the title character leaves the chamber of Duncan, having murdered the king, he believes he hears someone cry "Sleep no more: Macbeth doth murder sleep".

Macbeth is plagued by insomnia and his wife, Lady Macbeth, is prone to sleepwalking. As the play develops, Macbeth becomes increasingly paranoid that his misdeeds will be uncovered. The ghost of his old friend Banquo, who he has ordered to be killed, returns to haunt Macbeth, symbolising his guilty conscience.

Note: If no author is given, the source is cited instead.

• Sleep Disorder Research
• Insomnia Research
• Diseases and Conditions

• Sleep Disorders
• Insomnia
• Obstructive Sleep Apnea

• Paranoia
• Insomnia
• Sleep deprivation
• Delayed sleep phase syndrome
• Separation anxiety disorder
• Circadian rhythm sleep disorder