A seizure, the production of sudden and strong surges in electrochemical impulses by a group of nerves in the brain, can cause a loss of consciousness, or a blackout. Seizures are classified based on how much of the brain is involved, which part of the brain is involved and the intensity of the seizure. Although not all seizures result in blackouts, many types of seizures do cause a loss of consciousness.
Absence Seizures
Absence seizures, also called petit mal seizures, impair consciousness for only a few seconds. This type of seizure belongs to the classification known as generalized seizures, which affect both the left and right hemisphere of the brain.
Absence seizures may occur occasionally or as much as 100 times a day, according to the Epilepsy Foundation. The distinguishing characteristics of absence seizures include the absence of a preceding aura--the sensation the seizure will occur, an abrupt onset, a brief duration and a complete recovery. Other symptoms include automatisms--repetitive movements such as lip-smacking--a loss of muscle tone or jerky muscle contractions, usually involving the eyes or facial muscles.
Atonic Seizures
Atonic seizures, another type of generalized seizure, cause a complete loss of muscle tone. Atonic seizures can affect only a specific part of the body such as the head. Known as fragmentary atonic seizures, these result in isolated loss of muscle tone causing only the affected portion to go limp. Massive atonic seizures; however, affect the entire body, resulting in total collapse.
Some atonic seizures are classified as brief, resulting in a loss of consciousness lasting only a few seconds. Atonic seizures which cause the patient to collapse remaining motionless for a minute or more are classified as prolonged atonic seizures.
Tonic-Clonic Seizures
Tonic-clonic seizures are the most common and well known type of seizure, according to the Epilepsy Foundation. Tonic-clonic seizures involve the entire brain, classifying them as a generalized seizure. Formally known as grand mal seizures, this type of seizure involves a loss of consciousness along with a tonic state, in which the limbs stiffen followed by a clonic state, involving jerky muscle contractions in the limbs and face. The tonic state typically lasts around 10 to 20 seconds while the clonic state lasts up to two minutes, according to the Mayo Clinic.
Complex Partial Seizures
Unlike the above described seizures resulting in blackouts, complex partial seizures, also called complex focal seizures, affect just one part of the brain. Complex focal seizures are often preceded by auras, the sensation that the seizure will occur. Automatisms often occur during complex partial seizures, which typically last only a few seconds, according to the National Institute of Neurological Disorders and Stroke.
