High Heart Rate - Worried!

I saw my midwife at 27 weeks, first time since switching from Ob/Gym.
Anyway, she listened my babies heart rate and this time it was 162! She said it ok, but I might be dehydrated. I thought I was drinking enough water but of course now I'm drinking more.
She said if it was higher she might have done more testing. But I'm still so worried! Has this ever happened to anyone? I can't stop thinking something is wrong.