But the real explanation may lie deep within your genetic make-up.
A Dutch study has identified seven genes that put people at increased risk of developing sleeplessness.
Their discovery that a tendency to suffer from insomnia is biological rather than psychological gives hope to the third of UK adults who have sleep problems.
It means that targeted treatments could be developed, rather than the millions of prescriptions for sleeping tablets that are made out each year.
The research, by scientists at Vrije University in Amsterdam, was carried out by mapping the DNA of more than 113 000 people from Britain and the Netherlands. Sleep specialists Professor Eus van Someren said: “Insomnia is all too often dismissed as being ‘all in your head’. Our research brings a new perspective. Insomnia is also in the genes.”
The professor, whose work is published in the Nature Genetics journal, said he hoped the breakthrough would lead to more research into sleep problems, which he said had been neglected
“Compared with the severity, prevalence and risks of insomnia, only a few studies targeted its causes,” he said.
The team also discovered there were different genetic mutations linked to sleep for men and women, and that women were more susceptible to the problem.
They also found a strong genetic overlap with other traits such as anxiety disorders, depression, neuroticism and low well-being.
Anke Hammerschlag, a PhD student at the university, said: “This is an interesting finding, because these characteristics tend to go hand-in-hand with insomnia.
“We now know this is partly due to the shared genetic basis.”
Professor Danielle Posthuma, also at Vrije University, said there are also separate variants for men and women.
“Part of the genetic variants turned out to be different. This suggests that, for some part, different biological mechanisms may lead to insomnia in men and women,” Posthuma said.
“We also found a difference between men and women in terms of prevalence. In the sample we studied, including mainly people older than 50, 33% of the women suffered from insomnia. For men this was 24%.”
The risk genes were tracked down thanks to the UK Biobank, a health study which has recruited half a million people, aged 40 to 69, and makes data on DNA available. - Daily Mail