My Vivoactive 4S is shutting off in the middle of the night, even though it was charged two days ago (less than 40hrs wear time), and still had over 60% battery at bedtime. No activity had occurred in that time, no music playing, no pulse ox monitoring, screen is very dim, notifications are minimal.. Is anyone else experiencing this or know why it is happening? I've had it for 10mths and I used to get 5 days out of it. This is the second time this has occurred. Good thing I wasn't relying on it for an alarm!