Snoring is harmless. Five hours of sleep is enough. Alcohol before bed helps.
All of them were debunked as false in a peer-reviewed study of a team at New York University.
It was published in National Sleep Foundation's journal Sleep Health, BBC reports.
Myths spanned sleep duration, sleep timing, behaviors during sleep, daytime behaviors related to sleep, pre-sleep behaviors and brain function and sleep.
Sleep is a vital part of life that affects our productivity, mood, and general health and well-being," said Rebecca Robbins, lead investigator and postdoctoral research fellow at NYU Langone Health, in a statement.
Dispelling myths about sleep promotes healthier sleep habits which, in turn, promote overall better health."
The researchers said the belief that less than five hours' shut-eye was healthy, was one of the most damaging myths to health.
We have extensive evidence to show sleeping five hours or less consistently, increases your risk greatly for adverse health consequences," said researcher Dr Rebecca Robbins.
These included cardiovascular diseases, such as heart attacks and strokes, and shorter life expectancy. Instead, she recommends everyone should aim for a consistent seven to eight hours of sleep a night.
The relaxing nightcap is a myth, says the team, whether it's a glass of wine, a dram of whisky or a bottle of beer.
It may help you fall asleep, but it dramatically reduces the quality of your rest that night," said Dr Robbins.
It particularly disrupts your REM (rapid eye movement) stage of sleep, which is important for memory and learning.
Often if we're watching the television it's the nightly news… it's something that's going to cause you insomnia or stress right before bed when we're trying to power down and relax.", Dr Robbins argues.
The other issue with TV - along with smartphones and tablets - is they produce blue light, which can delay the body's production of the sleep hormone melatonin.
It does take the healthy sleeper about 15 minutes to fall asleep, but much longer than that… make sure to get out of bed, change the environment and do something that's mindlessq researchers explain.
But the research team says that when the alarm goes off, we should just get up.
Your body will go back to sleep, but it will be very light, low-quality sleep."
Instead the advice is to throw open the curtains and expose yourself to as much bright light as possible.
Snoring can be harmless, but it can also be a sign of the disorder sleep apnoea.
This causes the walls of the throat to relax and narrow during sleep, and can briefly stop people breathing.