Yes, I'd definitely get it checked out. I checked your previous post and noticed you're on Tramadol....that made me feel very speedy (can't remember if it actually raised my heartrate, but it bothered me enough to go off after a week or so.)
I do get Tachycardia occasionally, and my dr. never seems worried because it usually doesn't get above 120 - but otherwise, I'm on the slow side. Like you, it'll start out of the blue, sometimes when I sit up in bed in the morning. Wudda pain!
...fibromyalgia, hearing loss, elevated liver enzymes, skin grafting (back), arthritis, scoliosis, lumbar disc damage, sciatica, IBS, migraines, tachycardia, cancer surgeries (face).......I take Nortriptyline & Clonopin daily, and Darvocet as needed