A study is shining new light on a sleep disorder called "sleep drunkenness."

The disorder may be as prevalent as affecting one in every seven people.

Sleep drunkenness disorder involves confusion or inappropriate behavior, such as answering the phone instead of turning off the alarm, during or following arousals from sleep, either during the first part of the night or in the morning. An episode, often triggered by a forced awakening, may even cause violent behavior during sleep or amnesia of the episode.

"These episodes of waking up confused have received considerably less attention than sleepwalking even though the consequences can be just as serious," study author Maurice M. Ohayon said in a statement.

For the study, researchers interviewed more than 19,000 people aged 18 and older about their sleep habits and whether they had experienced any symptoms of the disorder. Participants were also asked about mental illness diagnoses and any medications they took.

They found that 15 percent of the group had experienced an episode in the last year, with more than half reporting more than one episode per week. In the majority of cases -- 84 percent -- people with sleep drunkenness also had a sleep disorder, a mental health disorder or were taking psychotropic drugs such as antidepressants. Less than 1 percent of the people with sleep drunkenness had no known cause or related condition.

Among those who had an episode, 37.4 percent also had a mental disorder. People with depression, bipolar disorder, alcoholism, panic or post-traumatic stress disorder and anxiety were more likely to experience sleep drunkenness.

The research also found that about 31 percent of people with sleep drunkenness were taking psychotropic medications such as antidepressants. Both long and short sleep times were associated with the sleep disorder. About 20 percent of those getting less than six hours of sleep per night and 15 percent of those getting at least nine hours experienced sleep drunkenness. People with sleep apnea also were more likely to have the disorder.

"These episodes of confused awakening have not gotten much attention, but given that they occur at a high rate in the general population, more research should be done on when they occur and whether they can be treated," Ohayon said. "People with sleep disorders or mental health issues should also be aware that they may be at greater risk of these episodes."

The findings were recently published in the journal Neurology.