Eh, what Cordex said. I've been on Provigil before to deal with excessive daytime sleepiness. It helps you stay awake in a much nicer manner than a normal "upper" (not habit forming, no high, no shakiness, no rapid heartrate). I could totally see a presidential candidate going on it to help deal with the effects of endless late hours and early mornings that come with candidacy.
Without some other emails or leaks that are Parkinsons specific, this one doesn't reveal much. Don't get me wrong, I think there are likely damaging things about her health that could be leaked/revealed, but this email doesn't reveal jack.