Seizures can also occur in people who do not have epilepsy for various reasons including brain trauma, drug use, elevated body temperature, low blood sugar and low levels of oxygen. Additionally, there are a number of conditions that look like epileptic seizures but are not.
5–10% of people who live to 80 years old have at least one epileptic seizure and the chance of experiencing a second seizure is between 40% and 50%. About 50% of patients with an unprovoked apparent "first seizure" have had other minor seizures, so their diagnosis is epilepsy. Epilepsy affects about 1% of the population currently and affected about 4% of the population at some point in time. Most of those affected—nearly 80%—live in developing countries.
The signs and symptoms of seizures vary depending on the type. The most common type of seizure is convulsive (60%). Two-thirds of these begin as focal seizures and become generalized while one third begin as generalized seizures. The remaining 40% of seizures are non-convulsive, an example of which is absence seizure. Duration or length of time a seizure lasts are also important in diagnosis and management, thus bystanders of a patient should time the event after summoning emergency personnel (unless the person is a known epileptic with a preferred management plan in place).
Jerking activity may start in a specific muscle group and spread to surrounding muscle groups—known as a Jacksonian march. Unusual activities that are not consciously created may occur. These are known as automatisms and include simple activities like smacking of the lips or more complex activities such as attempts to pick something up.