Can doctors tell me what does one feel during a heroin overdose?

U don't want to know: Forgive my frankness. Forget any ideas about "drifting peacefully off to sleep" as one might in the controlled euthanasia of a beloved pet using morphine, or an terminal sedation. The accidental heroin overdoses described by witnesses who are fellow-drug-abusers are often a horrible choking and a ghastly gush of foam from the lungs as the drug wrecks havoc on the deep chest nerves.