London - If it takes you more than half an hour to fall asleep at night, you may have a sleeping problem.
Waking up at night and taking more than 40 minutes to drift back off is another sign.
The first published guidance on what makes up a good night’s sleep suggests that many more of us are struggling than we might think.
The UK's National Sleep Foundation asked a panel of experts to examine 227 scientific studies, and they found that people who wake up more than once a night and sleep less than 85 percent of their time in bed are not getting good-quality slumber.
This could result in a greater risk of heart disease and diabetes, with not getting enough sleep also linked to putting on weight, fatigue and depression. It can also affect the fertility of couples trying for a baby.
A third of Britons suffer from poor sleep, with experts blaming stress, computers and taking work home with us.
The National Sleep Foundation’s guidelines suggest adults should not take longer than 30 minutes to fall asleep. Older people should be concerned if it takes them more than an hour to nod off.
The experts also say adults should not nap for more than 100 minutes at a time, and should not take more than four naps a day if they are sleeping properly.
Dr Max Hirshkowitz, of the US-based National Sleep Foundation, said the findings will help the millions of people using digital technology, such as Fitbits, to track how well they snooze.
He added: "These devices provide a glimpse into one’s sleep universe, which is otherwise unknown. These guidelines... make sense of it all – providing consumers with the resources needed to understand their sleep."
The new research, published in the journal Sleep Health, shows people should not spend any more than a quarter of their time in bed lying awake.
People who sleep well and are woken up in the night should take only up to 20 minutes to fall back to sleep.
Dr Maurice Ohayon, of the Stanford Sleep Epidemiology Research Centre, said: "In the past, we defined sleep by its negative outcomes. With this initiative, we are now on a better course towards defining sleep health."