Horses falling - HYPP?

[EAMULE@aol.com]

This is reaching into my faulty memory, but there is a disorder known as HYPP.
This genetic disorder causes horses to just collapse or fall.  It was strongly
connected to the Quarter Horse stallion Impressive who sired many Quarter
Horses and Appaloosas. 

All the above doesn't mean it is only found in QH and Apps.  

I have wondered if my now deceased QH stallion may have had this disorder in
his later years.  When he was 18 I would watch him walk across the pasture and
his front legs would go out from under him.  He could be standing still and
his legs would crumple.  He would just stand up again like nothing had
happened and continue on his way.

Hopefully there is someone out there who could add more knowledge than what I
have.  Vets...?

Ellen 
Memphis