When meditating or doing any exercises for breath control, it ALWAYS happens to me.... and I'm sober. By starting the journey into deep relaxation I have no choice but to consciously control my breathing or my body will stop on it's own. It's extremely annoying especially when I want to completely relax and not have to think about anything. It takes a while to revert back to autopilot. "Don't forget to breathe" - so cliche, but for me it really is true. Maybe it's more common than we think, but people are too afraid to admit it, fearing they have a respiratory problem such as apnea.... or it totally slips their mind to tell us that "oh, yeah, when you meditate you're gonna have to control your own breath whether you like it or not" hence the remind yourself to breathe tip.

It's only happened to me once while smoking.... it was the first time I ever got super stoned. Took one big hit, held it in, and a minute or so later I figured something was wrong.... then I realized I hadn't exhaled yet. Breathing was fine after that.

I have been able to meditate to get my breathing controlled to where I barely need to breathe at all and stay that way as long as I remain calm and focused. It's a trippy thing to experiment with when you're bored, like when trying to lower heart rate.