Sermorelin and heart rate issues

I've been taking prescription sermorelin on and off for years. Works nicely for me after I've been on it for awhile but I continue to have an unfortunate side effect: when I train my heart rate increases drastically as if I'm on stims. Even when lightly jogging it seems to skyrocket into 150-160 range and it induces anxiety and panic in me at that point and I usually have to take a knee or lay down. Any idea why this is happening? I take 300 mcg/night. Also take vitamin d3 at 2000 IU/day. The D used to give me a rapid heart beat too but proper magnesium supplementation corrected that. My resting heart rate is uneffected by all of this. It's always 55-65 BPM