What Causes Decrease In The BP Level While On Calcium Channel Blockers?

I accidentally took this med as prescribed, but I am afraid of it. It has pulled by bp from 174/93 to139/80 in 2 hours. My Pulse is 84. It shut my mom down twice. What if it continues to lower my bp?. I did not know it was a calcium channel blocker before I took it, but if I live I will not take any more. My doctor and I had discussed this and she seemed to think I should not take a calcium channel blocker, because of a mitral prolapse. She does not answer her phone.