Just as people are different, so are their sleeping habits. Some sleep long hours, while others manage with comparatively few. Not surprisingly, there are many popular beliefs about sleep that upon closer inspection turn out to be untrue.

Let's look at several frequent sleep-related claims and confirm their veracity – or not.

Checking time

True – you shouldn’t check the time if you’re having trouble falling asleep. Checking the time and calculating how many hours are left before you’ve got to get up is stressful, which is why the German Society for Sleep Research and Sleep Medicine (DGSM) says you shouldn’t have the time nearby if you often don’t sleep well.

"The pressure of having to sleep creates tension, which can make it even harder to fall asleep," it points out. Instead of lying awake and fretting, it advises getting out of bed for a while and putting your mind on something else.

After a vaccination

True – you should get plenty of sleep after a vaccination. Lack of sleep after a vaccination results in a lower antibody response. Researchers at the University of Pittsburgh in the United States found that people who slept less around the time of a hepatitis B vaccination built up a weaker immune defense than those who didn’t.

"You certainly should try to get sufficient, restorative sleep before and after a vaccination," remarks DGSM executive board member Dr. Anna Heidbreder.

Sleeping too much

The assumption that sleeping too much can lead to episodes of sleep paralysis is false. Sleep paralysis is a feeling of being awake but unable to move or speak as you are waking up or falling asleep, and can last up to several minutes, explains Dr. Hans-Günter Weess, who says it can be frightening because you don’t know when it will stop. Simply tapping a person in this state is normally enough to end it, he notes.

"Sleep paralysis is partly a continuation of REM (rapid eye movement) sleep during consciousness," he says. REM sleep, the sleep stage when you tend to have vivid dreams, also involves a loss of muscle control. This helps prevent you from acting out dreams and possibly injuring yourself or others.

Sleeping naked

Sleeping naked is not necessarily unhygienic. If all you wear under the covers is your birthday suit, you need to practice strict bed hygiene though, says Weess, director of the Sleep Disorders Center at the Palatinate Clinic for Psychiatry and Neurology in Klingenmünster, Germany.

"People lose one to two litres of water during sleep. So if you neglect proper hygiene, all sorts of little creatures, such as mites, can settle in your bed," he warns, and advises that nude sleepers change the bed linen at least once a week.

And what’s the ideal clothing if you don’t sleep in the buff? The main thing, he says, is that you’re "neither cold nor sweat, because both are stress factors and impair sleep."

Too little, too much

Too little sleep is unhealthy, but too much isn’t, is also a false assumption. You ought not to come anywhere near emulating koalas, long sleepers that may snooze between 18 and 22 hours a day. Just as regular sleep deficits aren’t good for you, so too is the opposite, according to the European Sleep Research Society. It says a sleep duration exceeding nine hours is too long for adults.

A study by the Onassis Cardiac Surgery Centre in Athens, Greece, showed that too much sleep can increase the risk of cardiovascular diseases such as heart attacks or strokes. But some illnesses, such as depression and sleep apnea, can cause a person to sleep longer than normal.

Six to eight hours

Six to eight hours of sleep a night are sufficient for everyone, is not entirely true. Sleep requirements vary from person to person. About 80% of us need between six and eight hours of sleep a night. "A lot of people don’t know how much sleep they need," Weess says. "They get up when the alarm clock rings."

To find out how much sleep your body really needs, he recommends not setting an alarm clock when you’re on holiday. Techniker Krankenkasse, the largest health insurance fund in Germany, has a rule of thumb: If you don’t get sleepy during the day while doing concentrated work, you’ve had enough sleep.