While On A Daily Walk, I Decided To Jog/run Up

While on a daily walk, I decided to jog/run up a small hill on my street. I have a Fitbit Charge HR with constant heart rate monitoring. At the top of the hill as I was walking again, my Fitbit showed 168bpm, then dropped to 132bpm for about a minute or so, then back to 165bpm, and did this bouncing around for about 10 minutes.
My initial thought was that my FitBit may be in error, but it has not shown any discrepancies in the past.
Is it possible that my heart could actually be fluctuating rate that drastically for so long? If so, what might be causing it?