Call it conversion disorder, call it hysteria (which I really do think has a bad history of being misused against women), whatever, but anyone who has ever been at the mercy of a crowd knows that crowd/mob/group behavior can and does take on a will of it's own. Think of historical situations like the crowds at the guillotines during the French Revolution; a couple like Bernardo and Homolka, or other serial killer pairs, where one party's past would give no indication of turning into a murderer/criminal without the pairing up with the other; mobs at the stores on black Friday... So many examples of this type of phenomenon on both large and small scales. People's behavior changing in groups.
Long ago I found myself in a crowd outside a rock concert venue - the doors weren't opening quick enough for some, and the temperature with windchill was well below zero. After a certain point, you could almost SEE a change sweep through the crowd. It started at the back, and moved forward up to the doors. In seconds I and my group found ourselves being squeezed tightly. People were falling down and couldn't get up, and almost a panic set in. Thank god no one was trampled, as they finally began opening all the doors, but I will never forget how you could practically SEE the change in behavior go through the crowd, spreading from back to front, everyone suddenly becoming impatient and rowdy and angry. Extremely scary.
I'm not saying there couldn't be a physical explanation for whatever is happening to these young women, but I'm also saying that mob/groupthink type behavior is very real, and I have no doubt that if that's what this is, then they aren't faking it, but it's a real psychological happening that is simply manifesting itself physically. I'm not sure why anyone would doubt that that can happen?