hey GR...Danzig pretty much covered it but since I know you like to know stuff...read this one...why tying up used to be called 'monday morning sickness'
http://www.suite101.com/article.cfm/horse_talk/61483
the trainers here could probably tell stories about 2 YO fillies that tie up...for some reason the high strung girls do it a lot...
yearling fillies like to do it at the sales too...when they did it was usually mild, we'd give them some bute paste, a little Ace to relax them, and some electrolytes...