Are tonic clonic seizures only a symptom of epilepsy?

No: There can be petit mal attacks =catatonic state. There can be isolated movements of certain body parts as well.

Epilepsy: is by definition recurrent unprovoked seizures. Recurrent provoked seizures are seen on occasion (for example the alcoholic who uses up his SSI monthly stipend who presents to the ER with alcohol withdrawal seizures on the 29th of the month) GTC seizures can occur for many reasons (taking too much Ultram, caffeine, cocaine, hypomagnesemia, hyponatremia, hypocalcemia, withdrawal from Benzodiazepine