Is It Safe To Take Bystolic To Lower BP And Pulse Rate?

I ve had muscle cramps forever, myofascial pain syndrome, Fibromyalgia, constant cramps everywhere. I do Deep tissue massage, acupuncture, Tens units, everything. Recently started Bystolic to lower BP and pulse rate. Noticed calves were a little worse for knots and curious if Bystolic could affect Potassium levels.