Okay, well all kinds of things can cause a high heart rate, so few of which are dangerous. If you're sick or having stomach issues, that can definitely contribute. If you're sick and dehydrated, that's another one. Dehydration is huge. Is the weather warmer where you are? That can make it worse.
High heart rate by itself is indicative of nothing. I get that pounding feeling sometimes, too, that's just how it is. Indigestion is a big culprit, and I would notice, when my anxiety was high and I noticed things like this, that if I could make myself burp, that my fast heart rate would decrease.
And when you say you have a fast heart rate, how fast are you talking? Also, I guarantee that now that you're focused on it, it's going to quicken as well. The heart's part of the parasympathetic nervous system, which means that it works whether we're conscious of it working or not—like breathing, we really have no control over it. But as it is, the more we pay attention, the wonkier it gets. Hard I know, but try not fixating on it, and I'm sure it'll go down.
If you're monitoring your heart rate and taking your pulse—stop it. Stop taking your temp, too. Health monitoring ramps up anxiety. Distraction, distraction, distraction is key. You might have this worry, but the more you can do to not indulge your worry, the better off you'll be.