Fainting goats!

[Goat Lover 3]

I have 2, female, five month fainting goats. The sire of these two is a Myotonic and the dams are Pygmies. I have these two kids in a shed that is about a foot off the ground. Almost every time Polly (one of the kids) tries to jump in the shed, she faints and falls out! I do have another shed that they can walk in, but it would be better if they could jump in this other shed. I don't want them getting hurt. Polly faints when another goats butts her, when she is trying to run, jump, or sometimes even when she's walking! This is my first time having Myotonic goats. Is this normal for Polly to stiffen so much??