Exhaustion, problems with alertness and overall crankiness are typical symptoms of not getting enough sleep, which for most people means anything less than seven or eight hours per night. But for natural "short sleepers," it's not a problem at all, as they are genetically wired to thrive on less sleep than the rest of us.
Those lucky people, who function just fine on six hours of sleep or less, constitute about one percent of the population, and researchers are trying to figure out what explains their unique trait. Someday, that scientific work might even lead to treatments that could help combat the effects of sleep deprivation.
Ying-Hui Fu, a professor at the University of California San Francisco School of Medicine, studies the genetics and other characteristics of short sleepers at her neurogenetics lab.
Currently, Fu knows of three types of genetic mutations that are related to the ability to function well on minimal amounts of sleep, which often runs in the family. In a 2009 paper published in the journal Science, she described a mother and a daughter who shared the same genetic mutation of the gene DEC2 that allowed them to thrive on six hours of sleep per night. So far Fu has identified about 50 families of short sleepers.
"This group of short sleepers is unique," Fu said, describing them as optimistic and energetic, often holding more than one job.
One of Fu's study subjects, a woman in her 90s, volunteers at a prison because she has so much time and energy that she feels compelled to somehow use it, Fu said, adding that another female short sleeper in her 80s often complains that she cannot find a man to keep up with her.
Even though researchers say that genetics appear to play a key role in short-sleepers' reduced need for sleep, there are still a number of unanswered questions.
"We don't understand why they are so optimistic and outgoing when they are supposed to be apathetic and irritable" on so little sleep, Dr. Christopher R. Jones, a professor at the Department of Neurology at the University of Utah who recruits short sleepers for scientific studies, told CBS News.
The connection between not needing much sleep and being full of energy is not completely clear to researchers, but mood, temperament and people's sleep patterns in general are often related, Fu said.
Interestingly, these high energy levels typical of short sleepers can sometimes reach behavioral extremes. For instance, a 2001 study published in the Journal of Sleep Research that examined the sleep patterns and personality of 12 short sleepers, researchers found some evidence of subclinical hypomania -- a milder form of manic behavior, characterized by euphoria, disinhibition and, in fact, a decreased need for sleep.
"That's our experience too," Jones said, describing the short sleepers he has met as "behaviorally activated." There may be something about this behavioral activation that helps short sleepers overcome sleepiness, he speculated.
Jones said many researchers think that short sleepers are actually sleep deprived but somehow just don't feel the symptoms of sleep deprivation the way most people do. The same Journal of Sleep Research study that showed evidence of hypomania also suggested that short sleepers get about half as many minutes of REM sleep -- the stage in the sleep cycle in which dreaming occurs -- as long sleepers.
Experts stress that it is important to distinguish between true short sleepers and people who actually need eight hours of sleep but force themselves to get by on less, which is much more common to encounter.
"I have never actually met a true short sleeper," Dr. Charles Bae, a sleep specialist at the Cleveland Clinic, told CBS News. "Most people who say they don't need a lot of sleep don't have that gene and they are just fooling themselves."
Moreover, for regular people, it is never a good idea to cut back on sleep. Previous research has shown that not getting the amount of sleep that your body requires can have negative consequences for your health. Sleep deprivation can compromise cognitive functioning and cardiovascular health and may raise your risk of cancer, Fu said, stressing that people should aim to get the amount of sleep that they know they need.
Research has even shown that people who do not get enough sleep have a higher overall risk of premature death, but this does not seem to apply to those natural short sleepers, experts say.
Researchers hope that someday, if they can figure out the mechanism and genetic pathways responsible for the short sleeping trait, it could lead to a drug that could potentially reduce the amount that ordinary people need. However, at this point, Fu thinks it's a rather distant prospect. "Everything is possible," she said. "It is just a matter of how long it takes."