Sleepwalkers may injure themselves while asleep but not wake up until morning.
People suffering from chronic pain often complain of disturbed sleep. Pain disrupts sleep by increasing the frequency of arousal. However, research has also suggested a different kind of link between pain and sleep disturbances.
Sleepwalking, or somnambulism, is a common sleep disorder about which little is known, and it affects up to 4% of adults.
It is classified as a "parasomnia," a sleep disorder involving undesirable physical events or experiences. Sleepwalking occurs during incomplete awakenings from deep sleep, also called short wave sleep (SWS). The sleeper walks and displays other complex behaviors while doing so.
The researchers, led by Dr. Regis Lopez, psychiatrist and sleep medicine specialist at Hospital Gui-de-Chauliac in Montpellier, France, studied 100 healthy control subjects and 100 patients with a diagnosis of sleepwalking, 55 of whom were males and 45 females, with a median age of 30 years.
Participants were assessed by a clinician and through self-report questionnaires for disease characteristics, sleep patterns, chronic pain, headache, migraine, depressive symptoms and quality of life, compared with 100 adult controls.
47% of the sleepwalkers were injured while asleep
Sleepwalkers reported headaches four times more frequently than non-sleepwalkers, and migraines 10 times more often, as well as higher levels of chronic pain, daytime sleepiness, and depressive and insomnia symptoms. After adjustments, however, sleepwalking was associated with increased risk for headache and migraine only.
But most surprising was the assessment of pain perception during injuries sustained while asleep.
Of the sleepwalkers, 47 reported having experienced at least one injurious sleepwalking episode. Only 10 reported waking immediately due to pain; the other 37 perceived no pain during the episode but felt pain later in the night or in the morning.
One patient sustained severe fractures after jumping out of a third-floor window while sleepwalking but did not feel the pain until after waking up later in the night.
Another broke his leg during a sleepwalking episode in which he climbed onto the roof of his house and fell down, but he did not wake up until morning.
Compared with pain-free sleepwalkers, sleepwalkers with chronic pain were more likely to be older and to have greater daytime sleepiness, insomnia and depressive symptoms.
Dr. Lopez says:
"Our most surprising result was the lack of pain perception during the sleepwalking episodes. We report here, for the first time, an analgesia phenomenon associated with sleepwalking."
He adds that, while the relationship between sleep and pain remains unclear, the results may help to understand why sleepwalking happens.
In a linked editorial, Dr. Michael Howell, of the Department of Neurology at the University of Minnesota in Minneapolis, comments that while remarkably little is known about sleepwalking, a recent surge in the condition has been noted alongside an increased use of sedative medications.
Regarding what causes sleepwalking, he says that many patients report "some disturbance that compels movement." Howell suggests that sleepwalking could be related to motor restlessness, like restless leg syndrome.
Limitations of the study include the fact that sleepwalking episodes are generally associated with lack of conscious awareness and memory of the event; the absence of perceived pain during parasomnia episodes could be due to a recall bias.
Medical News Today reported earlier this year on a possible genetic link for sleepwalking.