Fitbit says my heart rate is 120 while sitting. Should I be worried? Read below

Since 1pm today I have been on and off my feet moving and doing hard work. I moved my king size bed by myself and was just cleaning but moved everything out of my room. It is now 9 my time and my Fitbit either ranges from mid 90s to 120 while I’m sitting or laying down. I’m not normally this active and feel as if my body isn’t used to it. I’m also hypothyroid and severely out of shape and have a high BMI. I woke up feeling a bit out of it and achy this morning. Haven’t had much water but working on drinking more. Is there a chance it’s not accurate or if it is, should I be worried?