Concept:
Idiopathic epilepsy is a neurological disorder characterized by recurrent seizures without any identifiable structural cause in the brain. During seizures, abnormal electrical activity in the brain may lead to temporary disturbances in awareness and body control.
One of the most common and major symptoms associated with epilepsy is loss of consciousness.
Step 1: Understand the effect of epileptic seizures.
Epileptic seizures can interrupt normal brain functioning and may temporarily affect awareness and responsiveness.
Step 2: Identify the major symptom.
Among the given options, the most characteristic symptom of idiopathic epilepsy is:
\[
\text{loss of consciousness}
\]
Hence, the correct answer is:
\[
\boxed{(A)\ \text{loss of consciousness}}
\]