Are you getting enough sleep?

 The first we might ask then is what is a normal amount of sleep? The availability of artificial light since the 1840s has allowed us to be active beyond natural limits, taking away from the time we might be naturally asleep. The validity of this idea can be examined by looking at experiments of nature, societies that have no electricity to provide the artificial light that extends the useful day and exist as hunter-gatherers. In a study by UCLA’s Jerry Seigel three hunter gatherers societies were studied using activity monitors with light meters which found that the disparate societies show similar sleep parameters. They do not sleep more than modern humans with average durations of 5.7 to 7.1 hours; they go to sleep three hours after sunset and awake before sunrise, with ambient and body temperature driving these times. Little napping was seen.

In more agriculturally active, but still pre-industrial societies evidence points to “double sleeping” with bedtimes at sunset and frequent reports of waking after midnight, to be active by candlelight, and returning to sleep between 3am and five or 6am. Although the total sleep time is unknown it looks like the same seven hours but in two doses.

And today? National guidelines suggest we need 7 to 8 hours in our adult years and statistically that's true, and therefore most likely for you. But, for the individual contributing to the pool which gave rise to that average number, it may not be. So how do we know? The clinical answer is "the amount of sleep  needed to prevent sleepiness and to allow you to perform adequately without limitations in the day”. This can be easily judged when on vacation for example when, after a period of catch-up sleep, we fall into our natural routine and for most this will be 7 to 8 hours. But this definition is perhaps flawed since "performance" may be more subtly affected than just “performing adequate greatly without limitation in the day”. Sustained attention becomes more difficult with resulting sleep-related accidents (driving is the best example of the need for sustained attention) but subtler effects of lack of sufficient sleep are now becoming more evident. Examples abound, for example

There is a potential for an increase in in arguments at work because of labile emotions and reduced self control.

There is an increase in hunger due to well understood changes in the appetite hormones leptin and Grhelin. 

There are is also altered judgement which has produced for example changes in the outcome of court proceedings (sentences are more severe in the afternoon a time when prior lack of sleep increases sleepiness) and a lack of leadership skills in soldiers subject to sleep restriction. 

There's also a change in moral awareness made evident by a study of Google searches on the day after daylight saving time when people search less commonly for words with a moral content. 

And finally there are documented physical consequences of lack of sleep. There is an increased propensity to being susceptible to infections such as the common cold, to having poorer looking skin and to higher blood pressure.