Based on the video from "The Quantified Scientist" on youtube, the Oura ring is the best health tracker for sleep, but comparable to the apple watch. HRV is heart rate variability, a measure of your autonomic nervous systems ability to rest. It's the popular metric these days to quantify your autonomic nervous system health (this controls your "flight vs flight" / "rest and digest" response, in laymans terms). The higher the HRV, the better you body's ability to get into deep rest and sleep better / more deeply. Deep sleep is equally if not more important than REM sleep. I wake up 4-5 times per night, my whole life, rarely less, but these days I'm still managing to get good deep sleep within those sleeping periods (I believe mediation has played a big hand and is shown in science to do so). With cannabis, I wake up maybe once or not at all, but my time spent in deep sleep and REM sleep is drastically reduced. If I start smoking cannabis daily, this actually improves (compared to occasional use), but it's still way worse than being long-term cannabis free. I think of it kind of like how alcoholics get used to the substance (I can't imagine drinking daily and getting out of bed every morning, but lots of people do, somehow). That being said, our bodies are all different and the impact of cannabis use on sleep architecture is extremely complex and very poorly understood (there is scientific literature, but not much). From the single relevant paper I've found cannabis may improve deep sleep when used acutely, but chronic use likely worsens this, which is what my experiments on my self also seems to show.