Lack of sleep really can affect a person's sanity, with new research showing a clear link between insomnia and paranoid delusions.
Experts studying healthy volunteers and psychiatric patients found that 70% of ordinary people who scored highly for self-reported symptoms of paranoia had difficulty sleeping.
All of the psychiatric patients experienced feelings of persecution, and more than half of them suffered from moderate to severe insomnia.
Lead researcher Dr Daniel Freeman, from the Institute of Psychiatry at King's College London, said: "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.
"These are ideal conditions for paranoid fears to take hold. Regular, good quality sleep is important to our psychological wellbeing."
Insomnia is known to cause stress, anxiety and depression, which are themselves associated with paranoid thoughts.
Dr Freeman said the research, funded by the Wellcome Trust, suggested that tackling an inability to sleep could reduce the risk of paranoia.
"The good news is that there are several, tried-and-tested ways to overcome insomnia," he said. "A good night's sleep may simply make us view the world in a much more positive light."