QUESTION WITH JULIUS CAESAR BY WILLIAM SHAKESPEARE?!? paradox or metaphor?

It's metaphor. "Falling sickness" or "epilepsy" are perceived as weaknesses, a "seizure" of the mind, as it were. Cius is saying, essentially, that he, Casca and Brutus "seize" up and fail to take action - i.e., they are weak. Instead of taking the steps to remove Caesar from power, they are victims, at the moment, of temporary paralysis which keeps them from acting on their instincts.