This probably isn't quite the same thing, but this was my experience.

I went in for my check-up at 41 weeks and the hooked me up to check on bubs heart rate. It was strong and healthy most of the time, but occasionally dropped quite dramatically. They kept me on the monitors for hours and hours, before finally deciding to induce me (since I was 41 weeks already anyway). Inducing however made bubs worse, and his heart rate started dropping more often and for longer. I ended up with an emergency c/s.
This is pretty much how I ended up with my CS after being induced. DS had the cord wrapped around him.
This doesn't sound like the case with you though; in my case the HR was dropping with contractions.

I would be more inclined to think it is as Alan & Snacks said, just bub running out of room & being a bit quiet?

If you're really worried, why not pop up to hospital for a ctg? They won't mind & it can give you some peace of mind

I'm sure everything will be fine