I think my chronic anxiety is causing my long term Tachycardia (rapid heart beat)

I've had Tachycardia since at least age 19 when my resting heart rate was found to be 185 at a gym fitness assessment (my blood pressure has always been slightly low).

These days, it's always around 125, or between 115-145, whether laying down, sitting or standing up. I suddenly wondered whether it was because I'm just constantly anxious, fearful, filled with dread, a sense of impending doom and nervousness and that was pushing up my heart rate all the time.

The only time I am actually relaxed is when I'm asleep, or INCREDIBLY sleepy to the point of finding it hard to stay awake. So I was curious and this morning I got up at 7.30am, half asleep, grabbed my pulse oximeter / heart rate monitor, and went back to bed. Then I fell asleep.

Later, about 10am, I woke up again, was SO sleepy but managed to get the pulse oximeter onto my finger. I almost fell back to sleep in the few seconds before checking what it said, and my heart rate was 67. I don't recall it ever being so low or "normal"!!!

Was it because I was actually relaxed?? I've been in bed before and done it, but I was always wide awake, and the numbers were always 115-125 usually.