No sleeping on your back guidance is only after 28 weeks on Tommy's and they say not to worry if you roll onto your back as long as you go to sleep on your side.
If it was a big movement my guess would be baby moved into a position that you can't feel the movements as well (e.g. into the placenta). Mine does it frequently 😂. Personally I never find the whole eating/drinking sugary/cold things works to get movement. If baby is asleep or where wants to be nothing moves them - apart from if daddy talks/sings to them of course, then there is a decent chance they'll say hello to him!
My baby has a loose pattern of movements 6am - 9am, 11pm until I fall asleep then a few less defined smaller episodes throughout the day. Doesn't move if I walk a lot, I think motion rocks them to sleep. If I slept in and woke up at 10am I probably wouldn't get movements for a couple hours. If you're really concerned ring triage, they'll likely offer to let you come in and do a quick check of your vitals and quick doppler of baby to reassure you.
No matter what, can almost guarantee you rolling into your back has absolutely nothing to do with it. Even after 28 weeks the risk is still tiny.