My resting rate is in the 90's too.
Tachycardia can come from SOOO many thingsa-
caffeine, stress including poor sleep habits, food allergy, herbal supplements etc.
If you had the kind I have gotten, you basically feel like your heart is pounding while you sit still, like running a marathon.
It's a side effect to alot of meds - my asthma pills used to cause it once in a while.
So long as there is no pain, tingling, true difficulty breathing - it should pass if you lay and relax for a bit. Similar to anxiety attacks.
In the hospital we don't treat it unless the rate is staying over 150s and or the person has pain with it.
It sucks lol, and luckily I only get it once a year anymore if that - usually just a couple mins but I was a true caffeine diet pill junky in early 2000's and it would kick in just bending over to pick something up! Like 170's no problem and it went on for hours and hours. I would feel like I sprinted a 5k after a few hours.
I only got "cardioverted" once when it lasted 8 hrs, and the rate was 180-190. Since I walked in looking fine they didn't believe me- Then everyone's eyes bugged out I got raced to an ER bed, and they gave me Adenosine thru IV, which basically chemically stops the electricity in your heart so it can reset to a normal rate. It only lasts a few seconds, but scary to watch yourself flatline on the monitor lol.
Hey I was a medic so I found the process cool, but seriously - if it starts being more often, painful, or you started any new meds that could be it and you should def get it checked.