What defines an atonic seizure?

An atonic seizure is characterized by a sudden loss of muscle tone, which can lead to the individual collapsing or falling. This loss of muscle tone can affect the entire body or just a particular body part, resulting in a lack of postural control. Atonic seizures are sometimes referred to as "drop attacks" because the individual may suddenly drop to the ground due to the inability to maintain muscle strength.

The other options describe different types of seizure activity: rhythmic jerks are indicative of myoclonic seizures, chewing movements are often associated with focal seizures, and staring into space is typical of absence seizures. Each of these features serves to highlight the unique characteristics of specific seizure types, and none reflect the sudden loss of muscle tone seen in atonic seizures.