Well I phoned the midwife at my ob's practice and she said I should go in to get some CTG monitoring done.

The monitoring showed baby's heatbeat is fine. A baseline of about 135, going up to about 165 sometimes. Apparently there is nothing to worry about there.

So I'm much relieved, wondering whether I was being paranoid to start with, but I guess it's still "better safe than sorry", and baby and I both are better off if I'm not worrying about stuff like this.