What is normal sleep?
“What is normal sleep?” asks Dr Alison Bentley, Restonic Sleep Specialist. “It’s not a strange question really. But while books and Google insist that normal sleep is 7-8 hours long, in one go from 10pm to 6am, how many of us actually sleep like that? I find that people whose sleep differs from this ideal often believe they have a sleep disorder. However, that’s not necessarily the case.”
Dr Bentley, who has been seeing patients with sleep problems for 30 years and helped to run the first diagnostic sleep laboratory in South Africa, says there is some room for deviation from commonly cited “normal sleep”, in terms of three main components: duration, timing and solidity.
Duration
“In terms of duration, it is often quoted that 7-8 hours of sleep is the norm,” she says. “That is not quite true. When looking at the duration of sleep in a population, the average is 7-8 hours, but there are quite a few people who sleep less than that and others who need more sleep.”
Dr Bentley explains that if a person only sleeps five hours a night on average, they may either have insomnia or they may be a naturally short sleeper. The difference lies in how they function during the day. The naturally short sleeper copes well and doesn’t feel tired, while the person with insomnia feels tired and fatigued with a deficit in attention resulting in poor concentration and memory difficulties.
“If you are a naturally short sleeper there is no natural way to increase the number of hours slept and that is the ‘normal’ for you,” says Dr Bentley.
Timing
Similarly, while many people sleep between 10pm and 6am, there is variation in terms of timing. “Some people are like larks and go to bed early and wake early – feeling refreshed and ready to go to gym at 5am. Others are owls, preferring to stay up late and sleeping in a little later as well,” says Dr Bentley. “Whether you are a lark or an owl is also genetically determined. While it is possible to override your natural timing you will always feel a little jet-lagged. Owls can wake up at 5am, but will not wake up feeling refreshed and will instead feel tired and grumpy until their usual wake-up time.”
Solidity
Lastly, Dr Bentley says there’s also a misperception that “normal” sleep happens in one solid block – uninterrupted from start to finish.
“Solidity of sleep refers to the expectation that sleep during the night should occur in one solid block,” she says. “However, that never really happens because we actually wake up every 90 minutes.”
According to Dr Bentley, these wake-ups are very short and good sleepers don’t even remember them. It is believed that we wake up just to check the environment – an evolutionary “safety feature”.
“If you extend your sleep duration by an hour, those wake-ups are also likely to expand, meaning that when you wake up normally you may stay awake for longer,” she says. “Sometimes, the first three hours of sleep stay intact with multiple awakenings after that.”
While many assume that any period spent awake during the night must be abnormal, Dr Bentley says that literature from centuries ago suggests that it was normal to go to sleep as soon as it got dark, followed by a few hours spent awake during the night and another few hours of sleep before starting the day. “So, sleep would be in two pieces – and that was normal,” she says.
In conclusion, she summarises, sleep can be shorter or longer than 7-8 hours, occur earlier or later, and have gaps and still be normal.
“The most important thing is that you need to feel that you have had enough sleep when you wake up – you are not sleepy during the day. Good daytime function is a better measure of normal rather than the right numbers for your sleep at night,” she says.
Conversely, if you get the right numbers for your sleep but still feel tired and sleepy during the day that may indicate an important sleep disorder. If this is the case, consider speaking to a healthcare professional.