Seizures are usually some sort of electrical misfiring in the brain usually brought on by a chemical imbalance and is usually genetically inherited... is it a chance it could be a seizure... I can't say I don't know enough about frog physiology to guess. Blunt trauma can also bring on a seizure but I doubt you traumatized your frog. Could it have been spasms to mimic death throws as a defense mechnism... much more likely imo...