Almost all seizures are relatively brief, lasting from a few seconds to a few minutes. Most seizures last 2 to 5 minutes. When a seizure stops, the person may have a headache, sore muscles, unusual sensations, confusion, and profound fatigue. These after-effects are called the postictal state. In some people, one side of the body is weak, and the weakness lasts longer than the seizure (a condition called Todd's paralysis). Most people who have a seizure disorder look and behave normally between seizures and can live normal lives.

Symptoms vary depending on which area of the brain is affected by the abnormal electrical discharge (see Biology of the Nervous System: Brain and Brain Dysfunction: Dysfunction by Location). For example, if an abnormal electrical discharge occurs in the area that controls smell (located deep within temporal lobe), the person may sense an intensely pleasant or unpleasant smell. If it occurs in another area of the temporal lobe, the person may experience a sense of déjà vu, in which unfamiliar surroundings seem inexplicably familiar. If the abnormal discharge affects the frontal lobe, the person may be unable to speak. If the abnormal discharge affects large areas, it can cause a convulsion (jerking and spasms of muscles, usually throughout the body). Other symptoms include numbness or tingling in a specific body part, brief attacks of altered consciousness (such as drowsiness), loss of consciousness, confusion, and loss of muscle or bladder control.

Symptoms also vary depending on whether the seizure is partial (affecting only one side of the brain) or generalized (affecting large areas on both sides of the brain). Partial seizures may be simple, in which a person is completely conscious and aware of the surroundings, or complex, in which consciousness is impaired but not completely lost. Partial seizures include simple partial seizures, Jacksonian seizures, complex partial seizures, and epilepsia partialis continua. Generalized seizures cause a loss of consciousness and abnormal movements, usually immediately. Loss of consciousness may be brief or prolonged. Generalized seizures include tonic-clonic seizures, primary generalized epilepsy, absence seizures, atonic seizures, myoclonic seizures, and status epilepticus.

About 70% of people have only one type of seizure. The rest have two or more types. For example, some children who have juvenile myoclonic epilepsy also have tonic-clonic seizures and absence seizures in addition to the myoclonic seizures, which usually involve the arms.

In simple partial seizures, electrical discharges begin in a small area of the brain and remain confined to that area. Because only a small area of the brain is affected, symptoms are related to the function controlled by that area. For example, if the small area of the brain that controls the right arm's movements (in the left frontal lobe) is affected, the right arm may begin to shake and jerk. A simple partial seizure may progress to a complex partial seizure.

Jacksonian seizures produce symptoms that start in one part of the body, then spread to another. Abnormal movements may occur in the hand or foot, then "march up" the limb as the electrical activity spreads in the brain. The person is completely aware of what is occurring during the seizure. Thus, Jacksonian seizures are simple partial seizures.

Complex partial (psychomotor) seizures usually begin with an aura that lasts 1 to 2 minutes. During the aura, the person starts to lose touch with the surroundings. During or immediately after the aura, some people stare, move the arms and legs in strange and purposeless ways, utter meaningless sounds, do not understand what other people are saying, and resist help. Other people are able to converse, but their conversation lacks spontaneity, and the content is somewhat sparse. This state may last for several minutes. People may then recover fully. Or, the abnormal electrical discharge may spread to adjacent areas and to the other side of the brain. The result is a generalized seizure, which includes jerking of limbs, frothing at the mouth, and loss of consciousness.

Epilepsia partialis continua is a rare type of continuous or frequently recurring partial seizure, usually affecting a hand or the face. Seizures occur every few seconds or minutes for days to years at a time. These seizures usually result from localized damage (such as scarring due to a stroke) in adults or from inflammation of the brain (such as encephalitis and measles) in children.

Tonic-clonic (grand mal) seizures usually begin with an abnormal electrical discharge in a small area of the brain, resulting in a complex partial seizure. However, the discharge quickly spreads to adjoining parts of the brain, causing the entire area to malfunction. Primary generalized epilepsy begins with abnormal discharges in a large area of the brain. The abnormal discharges quickly spread to even more areas. In tonic-clonic seizures and primary generalized epilepsy, abnormal discharges result in a temporary loss of consciousness and a convulsion, with severe muscle spasms and jerking throughout the body. The head may forcefully turn to one side, the teeth may clench, the tongue is often bitten, and bladder control may be lost. The seizures usually last 1 to 2 minutes. Afterward, the person may have a headache, be temporarily confused, and feel extremely tired. Usually, the person does not remember what happened during the seizure.

Absence (petit mal) seizures begin in childhood, usually between the ages of 5 and 15. They do not produce the convulsions and other dramatic symptoms of tonic-clonic seizures. A person does not fall down, collapse, or move jerkily. Instead, the person has episodes of staring with fluttering eyelids and sometimes twitching facial muscles. The person is completely unaware of the surroundings. These episodes last 2 to 3 seconds and, rarely, 10 to 30 seconds. The person abruptly stops activity and resumes it just as abruptly, experiencing no after-effects and not knowing that a seizure has occurred.

Atonic seizures, which occur primarily in children, are characterized by complete loss of muscle tone and consciousness. They are brief, but they cause the child to collapse to the ground, increasing the risk of injury.

Myoclonic seizures are characterized by quick jerks of one or several limbs or the trunk. The seizures are brief and do not cause loss of consciousness, but they may occur repetitively.

In status epilepticus, the most serious seizure disorder and a medical emergency, the seizure does not stop. Electrical discharges occur throughout the brain. The discharges produce a generalized seizure lasting more than 15 minutes or recurring seizures between which the person does not completely regain consciousness. The person has convulsions with intense muscle contractions and cannot breathe adequately. Without rapid treatment, the heart and brain can become overtaxed and permanently damaged, and the person may die.

Seizures may have serious consequences. Intense, rapid muscle contractions can cause injuries, including broken bones. Sudden loss of consciousness can cause serious injury due to falls and accidents. The turbulent electrical activity of convulsive seizures that recur without recovery between them can cause brain damage. Most people who have a seizure disorder experience dozens or more seizures in their lives without serious brain damage. A single seizure does not impair intelligence, but recurring convulsive seizures may eventually do so.