A generalized seizure is a sudden change in consciousness, muscle control or behavior caused by abnormal activity in both sides of the brain. Generalized seizures are different from partial (focal) seizures, which usually occur in an isolated area in the brain. However, generalized seizures can sometimes begin with a partial seizure. This is called a partial onset seizure (or secondary generalized seizure). Some people may experience both partial and generalized seizures at different times. It is sometimes difficult to identify whether a seizure is partial or generalized.

Seizures are caused by a sudden increase in electrical activity in the brain. Neurons (nerve cells) produce electrochemical signals that instruct other parts of the body to perform certain actions, such as move and feel emotions or sensations.

A seizure occurs when some factor disturbs the pattern of electrochemical signals and causes the neurons to fire much faster than normal. This storm of electrical activity in the brain can result in the appearance of a seizure – changes in mood or behavior, hallucinations, involuntary muscle contractions or movement and loss of consciousness. During a generalized seizure, numerous symptoms may be experienced because the entire brain is affected. 

After a generalized seizure, it may take minutes or hours to return to full consciousness. Many people report a feeling of confusion or extreme tiredness. This is called postictal syndrome. Children who have a seizure may fall into a deep sleep after the seizure ends. This is normal and enables the brain to recover after the stress of the seizure. These children should not be woken during this time.

Some people with recurrent generalized seizures may experience a vague change of consciousness that occurs minutes or hours before they have a seizure. This sensation is called an aura. The exact nature of the aura is often unique to each individual, although it may include noticing a strange taste in the mouth, twitching in one limb or an inexplicable feeling of fear or apprehension. Because most people experience the same progression of events during each seizure, auras can serve as a warning sign that a seizure is going to occur.