The brain consists of more than 100 billion nerve cells. These all communicate with one another; some provoke others into sending further messages, while others tend to block them.
The proper working of the brain depends on a balance: too many nerve cells sending messages at once without enough being blocked can produce a sort of electrical storm - or a seizure.
Common causes include brain damage from birth injuries, head injuries, stroke, brain tumours and alcoholism. Some seizures probably have a genetic basis, although it's rare for epilepsy to run in families. However, no one cause has been found.
We're all at risk of developing epilepsy; in fact, each of us has a one in 50 chance of developing the condition at some point in our lives.
Seizures can occur without any obvious cause, but the risk is much greater in those who've had brain damage. These seizures can occur many years after the injury.
Certain recreational drugs and alcohol can induce seizures. And while the first seizures can be brought on by the drug in question, eventually spontaneous seizures may occur even after drug use has stopped.
Epilepsy, except in rare circumstances, isn't inherited, although the risk of developing epilepsy may be increased slightly in relatives of those who have the condition.
Seizures can take many forms and don't always involve losing consciousness or convulsions (when the muscles relax and tighten rhythmically). Most are sudden and short-lived, lasting a matter of seconds or minutes.
Simple partial seizures may be no more than the rhythmical twitching of part or all of a limb, an unusual taste, or a sensation of pins and needles in one part of the body. These can develop into other sorts of seizures, and are sometimes called 'warnings' or 'auras'.
Seizures should be considered as a possible cause of recurring episodes of confusion or strange behaviour, especially if the events are short-lived.
Absence seizures - a brief interruption of consciousness - should be suspected in children who are having repeated lapses in concentration lasting seconds.
Many myths and misconceptions surround epilepsy. Some date back to the Middle Ages, when seizures were thought to be a form of possession by spirits. Other myths have existed until more recent times, one being that epilepsy can be caused by masturbation, with castration used as a 'treatment'.