I bought a home checker partly because I am a hyprochondriac. Resting first thing in the morning is 48bpm. Resting during the day is 52-54bpm. My heart rate also drops dramatically quite quickly after exercise. Say I do 30-40 pressups etc etc.
Im also overweight for my height, 35yrs old. Wierd as I am sh1t on a bike (climbing etc). However I can carry heavy weights and I can carry a bike up a hill very easily with no probs.
If your heart rate takes along time to drop after a ride- get it checked. that is not right in my book.
90bpm resting- get it checked asap bunnyhop IF your normal resting rate is lower and its consistently 90 at the moment. Is it racing/spiking as well? Do you feel light-headed at any point?
Ps. You could be the fittest/healthiest person in the world and still suffer a heart attack IMO (if your thinking it cant be a prob).
Let a Doctor decide.