I have that occasionally, not as often as you describe though. Maybe a few times a year for me. And yes, like a sneeze, it feels good to release it.

It usually happens for me at non-obvious times, during a random conversation for example, but when it happens there is usually something non-obvious that was said that triggers it for me. Something emotional, not necessarily scary. Usually something i don't want to talk about so i try to hide the shudder sometimes or explain it away.

-- The world is what we make of it --
-- Dave
-- <A target="_blank" HREF=http://www.idexter.com>http://www.idexter.com</A>