Many people believe potentially harmful myths about epilepsy, a study from University College London suggests.
Seizures are caused by bursts of electrical activity in the brain
A third would put something in the mouth of a person having a seizure to stop them swallowing their tongue - but doing so could block their airways.
And 67% of the 4,605 people asked would call an ambulance immediately, Epilepsy and Behavior journal reports.
This is only needed for first seizures, those lasting over five minutes, if the person is hurt or has several seizures.
The authors questioned 4,605 staff and students from the university on what happens when someone has a seizure and how they should be helped.
Seizures are caused by sudden bursts of electrical activity in the brain, which stops the brain communicating normally with the body, and epilepsy is diagnosed in people who have regularly recurring seizures.
Symptoms depend on the type of seizure, and experts recommend that if someone has a seizure, objects around them are removed and their head is cushioned if they are on the floor.
Apart from that the seizure should be allowed to run its course.
The authors focused on four key myths surrounding seizures: the need to call an ambulance, the need to put something in their mouth so they do not swallow their tongue, and the incidence of foaming at the mouth and violence in seizures.
In fact, foaming and violence are not common symptoms of seizures but many people still believed these myths.
People aged over 65 were more likely to believe the myths than younger people.
For example, 30-35% of those aged under 65 would put something in the mouth of someone having a seizure, but 57% of respondents aged over 65 said they would do so.
The authors also found that awareness of the right things to do when someone has a seizure was higher in people who knew someone with epilepsy.
Risk of harm
Lead author Dr Sallie Baxendale said it was "extremely worrying" that so many people were still trying to put things in people's mouths during a seizure.
She said: "They think the person is going to swallow their tongue, but you can't actually do that.
"People having a seizure can bite down very hard, so something in their mouth could damage their teeth and leave them with a huge dental bill."
She said it could also damage the fingers of the person trying to help.
She added: "One problem is that seizures look extremely dramatic, but actually for most people it is something that happens occasionally and that they can recover from relatively quickly.
"The only thing to do is keep them safe and let the seizure run its course."
Alison Knight of charity Epilepsy Action said: "It is worrying that so many people do not know what to do, but in a way it's not surprising because epilepsy is still a very misunderstood condition."
The study authors suggest that the inaccurate depiction of epilepsy in films could help perpetuate these myths, and may contribute to negative stereotypes surrounding the condition.