High fetal heart rate

So today I went to my 36 week OB appointment. They were checking baby’s heart rate and it was bouncing between 165 and 185. They sent me for a non stress test at the hospital. I was hooked up for a good 25 minutes and baby’s heart rate was still 165 and fluctuating even into the 190s. Everything looked good with baby but they didn’t like how high it was. They took me off the machines and then about 20 mins later I went for an ultrasound. The baby was moving around in the ultrasound and they checked baby’s heart rate several times and it was down into the 140s. Everything else looked good so they eventually sent me home. I was just wondering if anyone else had this? Now I’m slightly freaked out about it.