A micro-sleep is a brief and unintended episode of sleep. It can cost you your life if it happens when you’re behind the wheel. Characterised by head snapping, nodding or closing your eyes, micro-sleeps commonly occur when you try to stay awake while performing monotonous tasks, including driving.
Micro-sleeps can last from a fraction of a second to a few minutes. During a four-second micro-sleep, a car travelling at 100 km/h will travel 111 metres while completely out of the driver’s control. The best way to avoid driving tired is to make sure you have enough sleep before driving, regardless of the length of your trip. There are three key sleep factors to consider before deciding whether or not to start driving – circadian rhythms, sleep debt and sleep inertia.
We are programmed by our body’s circadian rhythms to sleep at night and be awake during the day. During night-time hours and – to a lesser extent – during afternoon siesta hours, most types of human performance are impaired, including our ability to drive. Problems occur if we disrupt our natural sleep cycles, especially by staying awake during the night, and do not get enough sleep or suffer poor quality sleep.
Circadian rhythms cannot be reversed. Even if you have been working night shifts for many years, your body will still be programmed to sleep at night.
Older drivers tend to have more fatigue-related crashes during the afternoon siesta hours. Try to avoid driving at these times and watch out for the early warning signs.
Younger drivers tend to have more fatigue-related crashes during the night. Try to avoid driving between 10pm and 6am, when the fatigue crash risk is greater.
We all need about eight hours of sleep a night to function effectively. When we reduce the amount we sleep at night, we start to accumulate a sleep debt. It’s the difference between the hours of sleep you need and the hours you get. When we have sleep debt, our tendency to fall asleep the next day increases. The larger the sleep debt, the stronger the tendency to fall asleep – including when you are driving. Sleep debt can only be erased by having more sleep.
Sleep inertia is most dangerous for people who drive in the early morning hours, particularly shortly after waking from sleep. Sleep inertia is the feeling of grogginess you experience after waking. It can affect your ability to perform even simple tasks. It is usually reversed within 15 minutes by activity and noise. However, it can last up to four hours. Its severity depends on how much sleep you had and at what stage of the sleep cycle you awoke.