More people have a condition that makes them so sleepy that they can't work – even after a full night's sleep – than previously thought.
Researchers in the US estimate that as many as one in seventy people, or almost five million Americans, suffer from 'idiopathic hypersomnia'.
That is many times higher than previous estimates, which labeled the alleged disease as “rare” and said fewer than 200,000 people were affected.
There is controversy about idiopathic hypersomnia, which literally translates as unexplained sleepiness, but some doctors claim this does not exist.
Researchers in the US who surveyed hundreds of people suggested that as many as one in a hundred individuals, or more than a million people, had 'idiopathic hypersomnia' (stock image)
Of the 792 people surveyed – whose sleep quality was measured by a machine – scientists said a total of 12, or 1.5 percent, met the criteria to be diagnosed with the condition.
They also looked at data on daytime sleepiness among participants over a ten-year period, finding that 10 participants had chronic daytime sleepiness.
Researchers said the figures were evidence that the condition was 'relatively common' and 'more common than generally thought'.
Most of the study participants were obese, the data showed, and averaged about 59 years old. About half were women.
Dr. David Plante, a psychiatrist at the University of Wisconsin-Madison, said: 'Our results show that idiopathic hypersomnia is relatively common (and) more common than commonly thought.
'So there is probably a significant difference between the number of people with this condition and the number of people seeking treatment.'
He added: 'Further efforts to identify, diagnose and treat people with idiopathic hypersomnia are needed.
'Additional research may also clarify the causes of idiopathic hypersomnia and lead to new treatments.'
Patients with idiopathic hypersomnia are very sleepy during the day, even after sleeping for long periods of time at night and taking naps.
They also have difficulty waking up and when they wake up they immediately feel disoriented. Naps don't help refresh them.
Scientists say the condition makes daily activities such as working or picking up the children from school a challenge.
However, there is no single test to diagnose the condition, with the disease instead being a diagnosis 'of exclusion' – when other conditions have been ruled out.
Scientists say it could be caused by a hormonal imbalance that acts like an “all-day sleeping pill” or by problems with the circadian rhythm – or the body's sleep-wake cycle.
Treatment aims to relieve symptoms and may include giving them stimulant medications such as modafinil – brand name Provigil or Alertec – to help them stay awake during the day.
The condition differs from narcolepsy because, although people with it also feel tired, they do not sleep excessively and feel refreshed after a nap.
For the study, published in the journal Neurologyscientists attached the nearly 800 participants to a machine that measured their brain waves, blood oxygen levels, heart rate and breathing while they slept at night.
They also completed a daytime nap study, during which they were hooked up to the same machine while they fell asleep four to five times.
And participants were asked whether they ever felt tired during the day, how often they napped and how many hours of sleep they got on a work and non-work night.
The results also showed that participants with the condition took an average of four minutes to fall asleep at night and six minutes during naps.
For comparison, the overall figure was 13 minutes to fall asleep at night and 12 minutes during naps.
People with the disorder had more severe sleepiness, despite similar or longer sleep times, they said.
On a sleepiness survey that asked how likely a person is to fall asleep while sitting, talking or standing still in a car, people with the condition had an average score of 14 out of 24 – well above the 10 mark, prompting care is. .
By comparison, those without the condition had an average score of nine.
“It has been difficult to determine the prevalence of idiopathic hypersomnia because expensive and time-consuming sleep tests are required to diagnose it,” Dr. Plante added.
'We examined data from a large sleep study and found that this condition is much more common than previous estimates.
'(It's even) as common as some other common neurological and psychiatric conditions such as epilepsy, bipolar disorder and schizophrenia.'
An estimated 2.8 million Americans suffer from schizophrenia and 3.5 million from epilepsy.