Who, what, why: What is a micro-sleep?
Almost half of male drivers admit to experiencing micro-sleeps at the wheel. What are
they?
It's a "horrifying" statistic, according to road safety charity Brake.
Of 1,000 drivers it interviewed, 45% of men admitted to micro-sleeping while driving, as
did 22% of women. But what does this mean?
Micro-sleep is an episode of light sleep lasting five to 10 seconds. The brain goes to
sleep involuntarily and it is more likely to happen in a monotonous situation. People
wake suddenly, often with a sharp jerk of the head.
"Your eyelids start drooping and you start to lose contact with reality," says Prof Jim
Horne, director of Loughborough University's Sleep Research Centre. "You're asleep
for a few second, then wake up, often with a jolt."
Light sleep that lasts from five to 10 seconds during which the brain goes to
sleep involuntarily
This sudden head jerk is how people commonly know they've had a micro-sleep as the
brain doesn't remember such short naps.
"Sleep has to last beyond a minute or two for your brain to remember it," says Prof
Horne, who studied driver tiredness for 10 years. "With micro-sleep, you are just left
with a feeling of not knowing if you are coming or going."
It is caused, unsurprisingly, by fatigue. If episodes aren't tackled, they become more
frequent and last longer until you eventually fall into a proper sleep.
A head jolt in dangerous or inappropriate circumstances, like driving a car or in a
meeting, can sometimes prevent further episodes as the shock and realisation of what
has happened sends adrenaline pumping through the body
Drivers are particularly susceptible as driving can be monotonous. They are more at
risk in the afternoon as the body experiences a drop in energy levels, also at night
when a person is usually asleep.
Young drivers are also more at risk because young people need more sleep in general,
so are more impaired by sleep loss.
It's estimated that almost 20% of accidents on dull, major roads are sleep-related,
according to the Department for Transport. Drivers have no excuse, says Prof Horne.
"Sleep doesn't come from out of the blue. You can't be driving along alert one minute
and falling asleep the next. There's always adequate time to realise how sleepy you
are."
His advice, included in the Highway Code, is to safely park then have a drink
containing about 150mg of caffeine. It will not kick in for 20 minutes, so have a 15minute nap and then freshen up for five minutes before continuing your journey.
Reporting by Denise Winterman
Five things that stop a good night’s sleep
Tossing, turning, can't get to sleep? It's a familiar feeling for many. Here are five things
that could be preventing us from getting the restful night we need.
An uncomfortable or noisy environment
As we start to fall asleep, our muscle tone reduces and our limbs begin to relax. We
may feel drowsy but our brain is still active, and any noise or discomfort can make it
hard to fall asleep.
As we drift into light sleep, an area of the brain called the thalamus starts to block the
flow of information from our senses to the rest of the brain. But it will still let through
noises, which can wake us up.
After about half an hour of light sleep, most of us enter a type of deep sleep called
slow-wave sleep. The changes in the brain neurochemistry typical of deep sleep, make
it harder to be woken up. But some things will always get through - such as our names
being called out loudly.
Missing out on any part of our usual cycle of sleep results in reduced quality and
quantity of sleep.
An irregular routine
We all have a built-in body clock which tells us when we are tired, and helps
synchronise thousands of cells in our body to the circadian rhythm.
The main synchroniser for our body clock is light. Our eyes react to the light and dark,
even when our eyelids are closed.
Daylight prompts our brains to reduce the production of the sleep hormone melatonin.
We become more alert, and wake up.
If we sleep less, because of going to bed late or waking up early, we're unlikely to get
as much deep sleep as we need, or enough of the stage that comes after it - REM
(rapid eye movement) sleep, when we do most of our dreaming.
Stimulants - coffee, alcohol, food
Stages of sleep
Sleep is essential to maintaining normal levels of cognitive skills such as speech,
memory, and flexible thinking. Sleep plays a significant role in brain development.
Every 60-100 minutes we go through a cycle of four stages of sleep before entering
dream sleep
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•
•
•
Stage 1 is a drowsy, relaxed state between being awake and sleeping
Stage 2 is a period of light sleep where heart rate slows and body temperature
decreases, getting ready for deep sleep
Stage 3 and Stage 4, or deep sleep are hard to wake up from because there is
the lowest amount of activity in your brain and body
After deep sleep, we go back to Stage 2 and then enter dream sleep - also
called REM (rapid eye movement) sleep
Caffeine is a stimulant which can stay in our system for many hours. Drinks high in
caffeine make it harder to fall asleep and can result in more time in the lighter stages of
sleep, with less deep sleep.
Drinking alcohol often makes us snore more, making it harder to breathe, and so
making us more restless.
Although alcohol initially helps some of us fall asleep, too much of it may disrupt sleep.
A lot of alcohol close to bedtime means we can go straight into deep sleep, missing out
on the usual first stage of sleep.
As the alcohol starts to wear off, our bodies come out of deep sleep and back into REM
sleep, which is much easier to wake from.
In the course of a night we usually have six to seven cycles of REM sleep, which
leaves us feeling refreshed. However, a night of drinking means we'll typically have
only one to two, and wake up feeling exhausted.
Eating a large, heavy meal too close to bedtime may also interfere with sleep. Spicy or
fatty foods can cause heartburn, which leads to difficulty in falling asleep and
discomfort throughout the night.
Foods containing a chemical called tyramine (examples include bacon, cheese, nuts
and red wine) can keep us awake at night.
Tyramine causes the release of noradrenaline, a brain stimulant. Carbohydrates, such
as bread or pasta, have the opposite effect. They trigger the release of hormone
serotonin, which makes us sleepy.
The wrong body temperature
Our core body temperature goes down when we sleep. It's controlled by our body
clock, which starts to open up the blood vessels of the hands, face and feet, to lose
heat, as we approach the time we should be sleeping.
But if our bedrooms or duvets are too warm, our bodies can't lose heat. That can lead
to restlessness and discomfort.
Our core temperature should only be half a degree less than during the day. If we get
too cold, we get restless.
A busy mind
Stress is the enemy of sleep. In bed, our mind is left free to wander, and feeling
anxious about getting enough sleep will only make it worse.
In these states people lose track of time. You may nod off and wake up again but it
may still feel as if you are getting no sleep at all. This can result in fragmented sleep
with less time spent in the deep stages of sleep.
Sleep experts recommend getting up and doing an activity which distracts our mind
from worry - such as a puzzle - before trying to sleep again.