My body battery doesn't recharge?

I've had my Vivoactive 4S since Monday - I've slept for 7-8 hours every night. Tues I started with 44, yesterday 14 and today 4??!!! It doesn't seem to be recharging, I'm actually losing charge while I sleep. And my sleep isn't overly restless. Is there a setting I need to change or does it just take a while to work out my baseline?? I have got a cold but I definitely had more energy than 4 this morning?!!