Apple sleep thinks I am asleep when I am not wearing my watch

I remove my watch for a shower or hot tub. I look the next morning and notice great stats on sleep and deep sleep! Then I notice, the first recorded deep sleep is from when I was not even wearing the watch. In other words Apple health Sleep is saying I am asleep without even registering a heartbeat. This is absurd. I have read other similar questions from a while back, with no clear resolution except turning off sleep in watch settings, which defeats the purpose. The watch sleep settings are very simplistic, when what it needs at the very least is a choice to confirm sleep activity with heartbeat and slight motion. It states that it uses an algorithm to detect sleep through detecting movement from respiration, and heart beat, and clearly that is not the case. Anyone else run into the problem, and any real solutions? Is there an option somewhere to make sure Sleep uses heartbeat and respiration to detect sleep? It also makes me question sleep heart and respiratory stats, if over an hour of incorrectly identified sleep was actually devoid of any pulse or breath. Thanks for any help, i would like to use this watch and app to monitor what it claims to.