the process of heroin(opiate)overdose?

Well, I'm not a professional, but I know quite a bit.

When you shoot up too much heroin, first as always, pupils become very very small, then as you get more unconscious, you may have a stroke. Also, your body temperature dramatically drops until you completely loose consciousness. From then on, the body "forgets" to breathe OR more likely, the person is reflexively vomiting, but if it's lying on the back, the person chokes in it's own vomit. In that point, you can still save the person by shooting Naloxone (start with 3mg, can go up to 10) and intravenous if possible. If not, do it intramuscular, but it's going to take longer time until it begins to work and the time is critical. Without breathing, cardiovascular system fails too and from then on, only CPR can help the person.

So, the consciousness goes away first, respiratory rate is always low with heroin and is getting slower during the OD, pulse rate is also dropping dramatically, together with blood pressure and cardiac rhythm.

Hope this helped.

peace