An epileptic seizure, informally known as a seizure, is a period of symptoms due to abnormally excessive or synchronous neuronal activity in the brain. Outward effects vary from uncontrolled shaking movements involving much of the body with loss of consciousness (tonic-clonic seizure), to shaking movements involving only part of the body with variable levels of consciousness (focal seizure), to a subtle momentary loss of awareness (absence seizure). Most of the time these episodes last less than two minutes and it takes some time to return to normal. Loss of bladder control may occur.Seizures may be provoked and unprovoked. Provoked seizures are due to a temporary event such as low blood sugar, alcohol withdrawal, abusing alcohol together with prescription medication, low blood sodium, fever, brain infection, or concussion. Unprovoked seizures occur without a known or fixable cause such that ongoing seizures are likely. Unprovoked seizures may be exacerbated by stress or sleep deprivation. Epilepsy describes brain disease in which there has been at least one unprovoked seizure and where there is a high risk of additional seizures in the future. Conditions that look like epileptic seizures but are not include: fainting, nonepileptic psychogenic seizure  and tremor.A seizure that lasts for more than a brief period is a medical emergency. Any seizure lasting longer than five minutes should be treated as status epilepticus. A first seizure generally does not require long-term treatment with anti-seizure medications unless a specific problem is found on electroencephalogram (EEG) or brain imaging.
Very high body temperatures may also be a cause. Typically this requires a temperature greater than 42 °C (107.6 °F). Head injury may cause non-epileptic post-traumatic seizures or post-traumatic epilepsy
About 3.5 to 5.5% of people with celiac disease also have seizures. Seizures in a person with a shunt may indicate failure
Hemorrhagic stroke can occasionally present with seizures, embolic strokes generally do not (though epilepsy is a common later complication); cerebral venous sinus thrombosis, a rare type of stroke, is more likely to be accompanied by seizures than other types of stroke
Multiple sclerosis may cause seizures
Electroconvulsive therapy (ECT) deliberately sets out to induce a seizure for the treatment of major depression. Reflex seizure induced by a specific stimulus or trigger (extrinsic or intrinsic stimuli)

Mechanism
Normally, brain electrical activity is non-synchronous. In epileptic seizures, due to problems within the brain, a group of neurons begin firing in an abnormal, excessive, and synchronized manner. This results in a wave of depolarization known as a paroxysmal depolarizing shift.Normally after an excitatory neuron fires it becomes more resistant to firing for a period of time. This is due in part from the effect of inhibitory neurons, electrical changes within the excitatory neuron, and the negative effects of adenosine. In epilepsy the resistance of excitatory neurons to fire during this period is decreased. This may occur due to changes in ion channels or inhibitory neurons not functioning properly. Forty-one ion-channel genes and over 1,600 ion-channel mutations have been implicated in the development of epileptic seizure.