Thousands of people have been misdiagnosed with epilepsy, when fainting due to low blood pressure has been mistaken for a seizure.
Resarchers at the Manchester Royal Infirmary and Salford's Hope Hospital studied 900 patients over a four year period. Dr Adam Fitzpatrick told BBC News Online:
"These people are suffering from a cardiovascular condition which makes them faint because of a sudden drop in blood pressure.
"We don't know exactly how it is triggered but it is accompanied by a slowing heart rate. To the untutored eye it can appear that the people who are fainting are also having an epileptic fit.
"If they collapse in the street a witness may tell an ambulanceman they have seen someone having a fit and that misdiagnosis is passed on to casualty and then on to their GP."
He said correct diagnoses meant patients could be fitted with pacemakers and given effective drugs to counteract fainting.