This is why I don't use a collar:
http://www.marvistavet.com/html/body..._collapse.html
You can add using collars to the list of possibilities that start bringing out symptoms. Some say it does and some say it doesn't. It isn't worth the risk to me. Ellie used to wear a collar before I knew about this and I regret it now because I could have seriously injured her throat.
Collars around the house are fine but I prefer never to attach a leash to them. All collars and harnesses come off of Ellie when I go away.