A new study has shed some light on a disorder known as “sleep drunkenness.” The sleep disorder is quite common, and may affect as many as one in seven people in the U.S.

Sleep drunkenness – also known as “confusional arousal” – is a condition which causes people to wake up confused, not knowing where they are. They may injure themselves or others in severe cases.

The study involved interviewing 9,136 people age 18 years and older about their sleep habits, and whether or not they experience any other symptoms of the sleep disorder. They were also asked about any medications they take or any diagnoses for mental illness.

The researchers discovered that 15 percent of the participants in the study experienced an episode of sleep drunkenness in the past year, with over half claiming to have experienced more than one episode each week. Most of the participants with sleep drunkenness also had a sleep disorder, a mental health condition, or were on some type of psychotropic drug.

Study author Maurice M. Ohayon, MD, DSc, PhD, with Stanford University School of Medicine in Palo Alto, CA., says that these episodes have not received nearly enough attention, even though the ramifications can be serious.

“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. People with sleep disorders or mental health issues should also be aware that they may be at greater risk of these episodes,” said Ohayon in a statement.

The findings of the study are published in Neurology®, the medical journal of the American Academy of Neurology.