This sounds very stupidly dangerous. I’m amazed this is legal, and that people would do it in the first place. I get wanting to win at all costs but this is nuts.
I don't know what it is about cycling that seems to concentrate some of the most insane physiological manipulation (not sure if that's the right phrase tbh). Other sports like baseball/tennis/etc seem to have some issues with like general steroids. But the level that cyclists go to always seems to exceed them by orders of magnitude. I don't know how true it is, but I've heard that some cyclists had/have to set alarms…
Even as a casual runner (top 20% in a marathon, def not competitive), I have had to silence low heart rate alarms on my apple watch because my heart rate regularly drops below 40bpm at night. When I’m in peak condition for a race, I’ve seen it drop as low as 30.
Professional cyclists have the highest VO2max of any athlete. Even without drugs I would be completely unsurprised if their heart rate gets to 20bpm in deep sleep.