Have your doctors said it is not cataplexy? Were you tested for narcolepsy? It definitely sounds like cataplexy. You may want to post this in the sleep disorders forum:
to see if there are others there with Narcolepsy w/ Cataplexy who may be able to relate to your experience. When you say you "almost pass out," can you explain more specifically what you are experiencing? Do you get lightheaded during these episodes?
As you lose muscle control, do you drop to the ground? Are you paralyzed or too weak to get up for a period of time thereafter? Can you explain the episodes in more detail?
I have narcolepsy with cataplexy. Cataplexy is rare in the absence of narcolepsy, but I believe it is possible. You may want to get a referral to a sleep neurologist to rule out narcolepsy w/ cataplexy, even if you're not sure you have symptoms of it, especially if these attacks are bothersome to you.
The other thing you could be experiencing is presyncope, which can be accompanied by a loss of muscle tone as well as the sensation of almost passing out. I'm not sure how frequently presyncope is precipitated by emotions such as anger, but I suppose being startled or surprised could do it in a susceptible person (a form of situational syncope, I would guess). When you say your heart rate doesn't change, do you know because you are wearing a heart rate monitor at the time, or because you don't feel it changing? During presyncope, sometimes the heart rate will change (rising or dropping suddenly) while for others the heart rate remains constant and only the blood pressure changes (dropping suddenly--a vasodepressor syncope).
If your doctor honestly doesn't have a clue, you might mention the possibility of these being attacks of presyncope, and possibly request a tilt table test.
Here is some information that may be of help for you.
(This is a full length TV program but it gives good examples of differing experiences of cataplexy from milder to extremely severe:)