It’s not uncommon to meet an adult who sleeps less than six hours a night, but it is uncommon to meet one who feels rested after six hours of sleep or less. Contrary to popular belief, there is a small percentage of adults who don’t require the recommended seven hours of sleep each night. Someone like this is called a short sleeper, and they function well during the day even after sleeping less than six hours a night.

A short sleeper doesn’t restrict their amount of sleep like most others. This is not the same as your college friend who slept three hours a night in preparation for finals. It’s also different from most adults who are forced to cut sleeping short in order to wake up for work or balance other responsibilities.

Instead, a short sleeper’s (short) duration of sleep is consistent, even on weekends, and this doesn’t have a negative effect on them. This is not the same as insomnia, which occurs when a person has trouble falling or staying asleep. While a short sleeper’s friends and family might think they need more sleep, this is incorrect.

If a person constantly gets less sleep than is needed, they will suffer from insufficient sleep syndrome. The most common symptom is daytime sleepiness. A short sleeper will not experience this. Their quality of sleep will be good and they won’t need to take naps or “catch up” on sleep over the weekend.

Research is still being done on the topic, but it’s possible that short sleepers have a gene mutation allowing them to function well on six hours or less of sleep each night.

On the flipside, there are people who require more than seven hours of sleep each night to function well. A long sleeper will sleep much longer than others their age. Adult long sleepers will typically sleep for 10 to 12 hours a night. Their sleep quality is good and they don’t have any complaints. Long sleeping is consistent and not a result of a medication or a mental health condition.

While you may think that your teenager is staying in bed too long, this differs from the stable sleep pattern of a long sleeper. Many teens tend to restrict their sleep during the week and then binge sleep on the weekends. In contrast, long sleepers are not oversleeping as a result of a late night or irregular sleep pattern. Often their extensive need for sleep starts during childhood. There is nothing wrong with long sleepers; they just need more sleep than is normally required for most people.

During the week, a long sleeper usually needs to sleep less in order to perform daily tasks like going to a job or school. If they don’t get enough sleep, they will feel tired. This can negatively impact relationships and job performance. They may function alright on nine hours of sleep on the weeknights, and sleep between 12 and 15 hours on the weekends to make up for it.

It’s important to distinguish short and long sleep from a sleep disorder. Many sleep disorders such as sleep apnea and narcolepsy can involve daytime sleepiness. Other sleep disorders such as idiopathic hypersomnia can involve long periods of sleep. A long sleep duration also can be caused by other medical problems.

Talk to your doctor if you have a consistent sleep pattern but rarely feel refreshed during the day. Your doctor may refer you to an accredited sleep center for help.