Apple Watch not noticing I wake in the night

My Watch 8 seems pretty good at tracking time in bed, but seems to confuse sitting on the sofa with actual sleep time, depsite the fact I am talking, moving and taking a drink during this time. Although this is frustrating, the worst thing is that it doesn't recognise when I wake up in the night. I can forgive it if all I do is open my eyes and close them again, but the last 2 weeks I have had a terrible cold, and regulary wake up at 3 or 4am and have a coughing fit, which involves considerable movement, noise and I'd imagine quite a change in heart rate as I'm gasping for breath and barking like an asthmatic seal. When I look at my data, it says I've been in core sleep, and congratulates me on a good nights sleep. Surely the watch can't be that insensitive to my movement and heart rate, and if it is, what other features are as good as useless on it too?