Epilepsy is the tendency to have recurrent seizures, which tend to recur spontaneously. These seizures occur when there is an electrical disturbance in the brain, and the signals it sends to the body become mixed up, rather like an electrical storm in the brain.
There are many different types of seizure, usually divided into two categories - generalised or partial. Typically a seizure may last from a few seconds to a few minutes.
Partial seizure - affects only part of the brain. Consciousness is not lost in a simple partial seizure; consciousness is impaired in a complex partial seizure.
Generalised seizures affect the whole brain, and often involve a loss of consciousness. They include the Tonic Clonic seizure where the person falls down, and their body stiffens and shakes; the Atonic seizure where the body goes floppy rather than stiff; the Absence seizure, which usually shows itself in a blank stare lasting a few seconds; the Myoclonic seizure, which is very brief and involves a muscle jerk.