What Causes Elevated Diastolic Blood Pressure Levels?

An MD changed my Lisinopril to Losartan recently to see if I could stop a cough I have had for years on Lisinopril. I was told to keep track of my bp s. The diastolic has been consistently ranging from 94 to 99 daily, and the systolic is also elevated usually In the 140 s to 150 s. I passed in my two weeks of collecting bp data with these results, concerned about the risk for heart attack and stroke. I was told by the covering MD to just keep on keeping track, make an appointment with my regular MD, and if my diastolic got was 120 to call them or if my diastolic was 180 to call them. Is it me or is that ridiculously high, such as a hypertensive crisis state? My fiancée was told to monitor his bp s one month, and had suffered a heart attack, not shortly after...........what is your opinion of these bp s? Thank you very much for your time!