Doctors from Kings Mill Hospital in Nottinghamshire studied the case of a man who was admitted to hospital suffering confusion during the day and hallucinations at night.

Hospital staff originally thought the 65-year-old man, who also suffered bronchitis and was overweight, was suffering from dementia.

But he was referred to a specialist respiratory unit when his wife mentioned that he snored heavily, with periods of choking and breath-holding.

Doctors writing in the Lancet medical journal say they think the snoring problem interacted with the man's bronchitis to produce hallucinations.

Tests

The specialist respiratory unit found that he was suffering a condition known as obstructive sleep apnoea.

It occurs when a person's airway becomes constricted, causing them to snore loudly as they struggle for breath.

The unit's tests showed that the level of oxygen in the man's blood often dropped to very low concentrations while he was asleep.

The man was given oxygen via a mask while he slept and this alleviated the alarming symptoms for a year, after which time they returned.

He later suffered pancreatic failure, which was unconnected to his snoring, and died.

Common complaint

The doctors say sleep apnoea combined with bronchitis could cause progressive carbon dioxide retention, leading to the man's symptoms.

They write: "Obstructive sleep apnoea is common, with prevalence estimates in the adult male population of about 1%.