One in seven people may be affected by what is termed sleep drunkenness, which leads to confused and disoriented behaviour when forced awake.

US researchers have found that 15% of people in their study had experienced an episode of 'sleep drunkenness' during the previous year.

The condition involves difficulty waking up which results in confusion or odd behaviour, such as answering the phone instead of turning off the alarm.

An episode may even cause amnesia about the confused behaviour.

Most of us are people are briefly disoriented when awakened suddenly from a deep sleep. However,  people who suffer from sleep drunkenness, or confusional arousal, may be in a confused and disoriented state for up to half an hour or more.

The researchers say this disorder has received less attention than the better-known sleepwalking, although its consequences can be just as serious.

The study looked at 19,136 people age 18 and older from the US population, who were interviewed about their sleep habits and whether they had experienced any symptoms of the sleep drunkenness disorder.

They were also asked about mental illness diagnoses in the past and any medications they took.

The study found that 15% 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-over 80% of people with sleep drunkenness also had a sleep disorder, a mental health disorder or were taking drugs such as antidepressants.

The study found sleep drunkenness may be linked to sleep disorders - either getting too little sleep or too much sleep.

This can can upset the body's rhythms which regulate sleep cycles.

The study is published in the journal Neurology.