The media has done a great job of making people believe that if you take heroin or fentanyl, you will immediately drop died. This is partly true but there are a few factors with this ideology people miss! If you have a clean system, your 1st relationship with this drug will be a beautiful one.(I hate to describe it like that but it's true). If you are lucky to OD, your natural instincts will kick in and you will vomit

Since this a suicide forum I'm assuming death is your goal. Well, all you can do at this point is hope your vomit cause you to aspirate (choke on your vomit) and die!
I don't think this is a reliable method and I personally think you'll turn into an addict before you die from the 1st dose. Just my opinion, take it for what it's worth.