Have you ever been drifting off to sleep, only to be jerked awake by the sound of a bomb going off inside your head? If you have, then you have most likely experienced exploding head syndrome, a mysterious and poorly understood sleep disorder. Exploding head syndrome (EHS) belongs to a family of sleep disorders known as parasomnias. Other parasomnias include sleep paralysis and hypnic jerks - the cause of that unpleasant feeling of falling we sometimes experience when drifting off to sleep.
Author
Dan Denis
Lecturer in Psychology, University of York
EHS has been known to medical professionals since at least 1876, and apparently the French philosopher and scientist René Descartes experienced it. Despite that, we know surprisingly little about the condition.
A typical episode is characterised by the experience of an abrupt loud noise or a sense of an explosion inside the head that occurs during the transition from wakefulness to sleep. The sounds that are heard during EHS are variable, and include perceptions of gun shots, doors slamming, or nondescript screaming. Importantly, the sounds that are heard are always short (a few seconds or less), very loud and without any obvious external source in the environment.
Alongside the sounds, some people experience accompanying brief visual hallucinations such as bright flashes. Others have also reported feelings of intense heat, or the sensation of electrical charge flowing through the upper body.
It is hard to estimate exactly many people experience EHS. One reason for this is simply a lack of available data. Only a handful of studies have attempted to survey the prevalence of EHS in the general population.
One early study found that 11% of otherwise healthy adults experienced EHS, while another study in undergraduate students found 17% of participants had experienced multiple episodes in their lifetime. In my own, more recent study, again in undergraduate students, my colleagues and I found that one-third of our sample had experienced at least one episode of EHS in their lifetime, with around 6% experiencing at least one episode a month.
What these studies show is that EHS is a relatively common experience, at least in young adults. It does however appear to be less common than other parasomnias such as hypnic jerks, which occur in up to 70% of people.
Triggers
The exact cause of EHS is unknown. While many theories of the root cause of EHS have been put forward, the most popular implicates the natural brain processes that are ongoing in the transition from wakefulness to sleep. On a typical night, as we transition from wakefulness into sleep, activity within the reticular formation of the brain is reduced.
The reticular formation is a set of brain structures located primarily in the brainstem and hypothalamus, that acts as an "on-off" switch for the brain. As reticular activity slows down in the transition to sleep, our sensory cortices that govern vision, sound, and motor movement start to shut down.
It has been proposed that the experience of EHS is due to a disruption in this normal switching-off process, which gives rise to delayed and disjointed surge of neuronal activation to sensory networks in the absence of any external stimuli. These brief surges of activation are then perceived as the loud, nondescript sounds that characterise EHS.
Although the exact neural basis of EHS remains speculative, we are starting to learn more about other factors that make an EHS episode more likely to happen. In one of the first studies to look at associated factors, my colleagues and I found that wellbeing variables such as life stress were associated with experiencing EHS. This relationship was mediated by symptoms of insomnia. In other words, life stress did not directly relate to EHS, but was related indirectly through first disrupting normal sleep patterns.
Is EHS dangerous?
Despite its provocative name, EHS is harmless. It is however important to distinguish an episode of EHS from other conditions, particularly from various types of headaches. EHS episodes are very short (several seconds) and usually there is no associated pain. If there is, it is mild and transient. In contrast, many headaches are longer-lasting and are associated with significantly higher levels of pain.
This is not to say that EHS cannot be a scary experience. In a recent survey of over 3,000 participants who had experienced EHS, we found that 45% of respondents reported moderate to severe levels of fear associated with their EHS. A quarter of participants also reported high levels of distress in response to experiencing EHS, with increased levels of distress associated with more frequent episodes.
Unfortunately, there have been no systematic studies investigating potential treatments and coping strategies for those struggling with distressing experiences of EHS. In our survey, participants reported that changing their sleeping position to avoid sleeping on their back, adjusting their sleep patterns and deploying mindfulness techniques were all effective strategies for preventing EHS. Whether any of these techniques prove to be effective in clinical trials remains to be seen.
Encouragingly, simply learning that EHS is a common and harmless condition can go a long way. In a patient case study, it was reported that reassurance and education about the experience stopped the episodes from happening. For now at least, the best advice seems to be to try and realise these experiences are natural and they don't indicate that anything is wrong. Simple techniques, such as improving sleep habits, may go a long way to preventing distressing episodes from occurring.
Dan Denis does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.
