Interesting, I found this post linked from the Hysteria page on Wikipedia: Joseph Mortimer Granville originally marketed his "percusser" invention for the relief of muscle aches, and it was hysteria doctors who found new uses for it in their practices.
I did have a feeling while watching the film that it was fiction, despite its "based on a true story" title at the beginning. It was just too convenient for him to have a rich friend already working with electricity, and clearly they just made up the Dalrymple characters as a convenient microcosm of the hysteria issue. Still, it was an enjoyable film with good humor. I'm considering going to see it again.