What is the primary symptom of a tonic-clonic generalized seizure?

The primary symptom of a tonic-clonic generalized seizure, commonly known as a grand mal seizure, involves two distinct phases: the tonic phase and the clonic phase. During the tonic phase, there is a sudden stiffening of the body as the muscles contract, which can lead to the person losing consciousness and falling. This is followed by the clonic phase, characterized by rapid rhythmic jerking movements of the body, particularly in the arms and legs.

This combination of body stiffening and subsequent jerking is a hallmark of tonic-clonic seizures and distinguishes them from other types of seizures. In contrast, staring into space typically indicates a different type of seizure known as an absence seizure, localized muscle twitching may be indicative of a focal seizure, and loss of balance can occur due to various reasons, but it is not specific to tonic-clonic seizures. The defining features of body stiffening and jerking movements are what make the selected answer correct.