While research on sleep disorders is ongoing, as is research dealing with genetics, there is some early evidence to indicate that sleepiness may be genetic to some degree. Research conducted on pairs of twins did indicate a high level of correlation with regard to lack of sleep or feelings of fatigue and being tired. Recent research has also found a genetic variant that may be responsible for many people who are unable to feel rested after sleeping, regardless of time spent sleeping. There are also many environmental factors that can affect sleepiness, and genetic factors usually deal with excessive feelings of tiredness despite time spent sleeping.
Sleepiness is generally described as a feeling of fatigue, being tired, and being unable to remain awake during the day. Excessive sleepiness is often associated with an inability to feel fully rested and frequently falling asleep throughout a day, regardless of how much time a person may spend sleeping. As mankind’s understanding of genetics has improved throughout the late 20th and early 21st centuries, some connections between such feelings and genetics have been found.
One famous research study looked at pairs of twins to see if there was a high correlation between each twin and feelings of sleepiness. The study found that there did seem to be a trend in which feelings of fatigue or being tired during the day were more common in one twin if the other twin experienced such feelings as well. This indicates that there could be a genetic cause of these feelings and that someone may experience feeling tired regardless of how much sleep he or she receives due to a genetic predisposition.
More recent research has found a genetic variant that may be the cause of such sleepiness. One gene in particular seems to indicate whether a person is more likely to feel sleepy than someone else, regardless of the amount of sleep that person has received. It is believed that about 25% of the general public may have this genetic variant, though these people do not all necessarily experience such feelings of sleepiness, but merely have the potential for it. The research indicates that these individuals often sleep more lightly and may wake up frequently throughout a period of sleep.
Excessive sleepiness is usually described as feelings of being tired or fatigued that exist while awake regardless of how much sleep a person receives. If someone only sleeps for four hours a day for three days in a row, then he or she is likely to feel sleepy due to these environmental causes. Someone who feels sleepy after three or four days of nine hours of sleep each night, however, may have a sleeping disorder.