Why epilepsy?

I think he was just telling the story? I mean, Snowden decided not to take the job in Hawaii because his girlfriend didn't want to move, but then she was okay with it because she thought it would help relieve the stress that had brought on the epilepsy.

Because Snowden actually has epilepsy? This is true story, and Stone told it very much like a documentary. He even used digital camera, which he previously used for documentaries alone.

"Was Stone implying that epileptics are untrustworthy?"

Are you even being serious?

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"I might be a Gung-Fu expert... but I need cash!"

I think that the suggestion is that Snowden stopped taking the meds that would have allowed him to live "a fairly normal life" because they made him less sharp (I've heard that this is a common complaint) and he needed to be as sharp as possible in order to fight the Chinese cyberattacks on the country he was defending. In the movie, it seems intended as another demonstration of his patriotism and his drive to do a vital job, one that he thought he alone could do, for his country.

It was obviously a fairly important issue in his life (and implied by the initial talk with the doctor about the medication that his mother was epileptic as well), so I don't see why it wouldn't be mentioned as a part of his personal life.

I guess the same reason the show "Rome" showed Julius Caesar suffering the same. It's an interesting detail about their lives.