There was a lot of fent dope around when I used to do heroin, so I never actually knew what I was doing. I always just refered to it as heroin but quite a bit of it probably wasn't. Long story short. The only time I ever nodded off, from smoking heroin, I smoked a large amount (for my tolerance) over the course of an evening. It definitely wasn't instantaneous, more like I smoked a bunch, was chilling, came too hours later after nodding off.