Sometimes it isn’t how much sleep you got that’s important, but how much sleep you think you got.
Our own perception of how much we slept during a night can be startlingly inaccurate. Dr Allison Harvey (now of UC Berkley) took insomniacs and measured how much they actually slept during the night. Despite the insomniacs reporting that they had only slept for two or three hours, they had in fact been asleep for an average of 7 hours – only 35 minutes less than a control group who didn’t have any problems sleeping.
This shows that insomniacs (and probably the rest of us) are very bad at judging the time it takes us to get to sleep, and the time we actually are asleep. It also suggests that worrying about sleep, and our beliefs about how we’ve slept, have a big role in the negative affects of what (we believe) is a sleepless night.
To test this Dr Harvey attached monitoring sensors to insomniacs which gave them a read-out in the morning of how much they had slept the night before. Except that the read-out was a lie and always told the participants in the experiments that they had slept ‘okay’ regardless of how badly they had slept. (In the seminar where I heard Dr Harvey discuss this research she told us that originally they tried giving false-feedback saying that the insomniacs had slept ‘excellently’ each night, but they just didn’t believe it so the researchers settled for just ‘okay’).
And what happened? When asked about how they felt, about their mood and alertness, those people who were lied to and told (by a scientific measurement, no less) that they had got a normal night’s sleep felt better for it!
So, it seems, one of the surprising disadvantages of trying to get enough sleep is that you can be hypersensitive to those times you don’t get enough – and that the hypersensitivity alone can depress and distract you.
Another entirely separate study shows neatly the role of anxiety in insomnia. A placebo effect is where something works because we believe it will work, not because of any intrinsic quality the thing itself has (there’s lots more on placebos in the book). Placebos are known to be potentially very strong – for example in one study of placebo painkillers a significant proportion of people found the placebo to have as strong an effect on their pain as morphine.
Anyway, what would we expect if we gave someone a pill and told them that it was a strong stimulant – something like eight cups of espresso – just before they went to bed? Well if they were normal we’d expect them to take longer to get to sleep, and that’s what happens. But if they’re an insomniac then they get to sleep quicker than they do normally. Why? Because, the theory goes, the insomniac is preventing from getting to sleep by their anxiety about getting to sleep (there’s lots of other work on this, including research by Dr Harvey). When they are given the fake eight-shots-of-espresso pill they are still anxious, but now they can put it down to the pill – “I’m awake, but hey – of course I’m awake, I had that pill” – now, because they’re not worrying about it, they fall off to sleep. Genius!
All this says, to me, that the best thing to do about not being able to sleep – or about not having had enough sleep – is to not worry about it, especially if the hours you have available to spend unconscious are out of your control. Often self-awareness is a good thing, but when it comes to sleep, both before and after, a little less self-awareness can do a lot of good.
(I should apologies for the lack of references in this post. I heard the material about inaccuracy of sleep perception in a seminar Dr Harvey gave at the University of Sheffield in 2003, and haven’t been able to find my notes, or any published details of the study. My apologies for any errors that have crept in. People wishing to follow this up could start with this paper  which shows that students with insomnia improved after they were shown the discrepancy between their perception and a more objective measure of how much they sleep. The placebo study I read in a textbook and unfortunately can’t remember where. You can buy one of the gadgets researchers use to measure sleep here and you can read The Onion‘s advice on fighting insomnia here).
1. Tang, N.K.Y. & Harvey, A.G. (2004). Correcting distorted perception of sleep in insomnia: a novel behavioural experiment? Behaviour Research and Therapy, 42, 27-39.