Manual Apple Watch sleep mode turns itself off for no reason some days

Most people don't seem to realize that you can turn on sleep mode manually and turn it off manually and you do not need to use the schedule AT ALL. Having said that, that is the way I operate because I was tired of fighting with the scheduled version, which spends a lot of time trying to wake me up in the middle of the night with haptics for no reason except it has decided that I am awake because I went to the bathroom or something. When you set your sleep mode manually you are then supposed to turn it off manually and that is what happens nine days out of 10. On the 10th day figuratively speaking but in fact on any random day I wake up and it's turned itself off for absolutely no reason. Sometimes I have no recordings and sometimes I have recordings that last until some very early time and then stop. I have absolutely no schedule set up in my phone anywhere. That is not the reason. It's just turning itself off without any reason that I know of. I'm not awake nothing is happening there is no schedule to wake it up there are no alarms. Why does it keep turning off? I am an insomniac and it's very important to me to keep these records for my doctors.