Anyone else experience a drop in heart rate - I am normally between 50-60 BPM

About 2 hours after I take 10mg my heart rate drops into the 40s, I spoke to the doc and he wanted to change me to something else as a precaution but I wanted to give this time to work and said well as long as he is happy I'll carry on. We agreed to monitor it.

I feel like I am coming up on a certain Class A drug when I take this stuff, get all the classic signs. Its very odd.