What Causes Dizziness And Reduced BP Level?

Is it possible for blood pressure to go too low. I am finding I am somewhat lightheaded and on taking my bp, which I try to do at least once a week, find it is in 115 to 120 range and it used to be in the mid 120 s I am on adalat xl 20 mg and hydrochlorothiazide 12.5 mg per day. I do not take any other medications. Bottom rate is anywhere from 60 to 75. low 70 s where it used to be