That reference that someone posted earlier, about the serotonin syndrome, is actually very good. And of course one of the main diagnostic features of the syndrome is clonus, including ocular (eye) clonus, and general muscle clonus.
Clonus is a series of rhythmic contractions of muscles - in other words, similar to an epileptic fit or seizure. There are other components too - all of which would make it extremely difficult to walk 14Km - or to do anything at all, actually.
It will be interesting to hear what the defence forensic toxicologist will say, and even more interesting to see if the prosecution have anticipated what he'll say and are prepared well enough to cross-examine him. And to make the point understandable to the jury without being patronizing. They really do need to see these finer points for what they are, and to appreciate the significance of them, how important they are, in differentiating between the defence's version of events and that of the prosecution.
I also hope that the judge is up with it too - I'm sure he would be. And I hope he is able to give guidance to the jury if he sense that some of the technical details are going over their heads. I hope.....
One thing that occurred to me is if Allison suffered hyperthermia from Serotonin Syndrome, she'd likely have torn that jacket off.