High diastolic reading

What would cause an increase in my diastolic reading and my systolic stay the same .
My age is 68, height 6'-4", weight 240 lbs.,  health is excellent. My normal blood pressure is 110/65 - heart rate 60. Sometimes now I feel dizzy and when I check my blood pressure, it will be 110/95 or 115/97 - my heart rate stays the same. My stress level is high . My wife passed away in 2005 at the young age of 53. This was from complications of diabetes.  Due mainly to the fact that Eli-Lilly stop manufacturing her insulin.
Is this change in the diastolic reading normal?  My father-in-law's heart doctor stated to him that he does not get excited when someones diastolic heading gets high. He stated that he only is concerned about the high systolic reading.

[Cleveland Clinic]

Diastolic blood pressure is as important as systolic.  In fact it is more strongly linked to stroke. I am very aggressive in controlling both.  This isolated diastolic elevation is atypical but may be related to high catecholamine state and elevated intravascular volume.  You definitely have to address your high stress level and also try to cut down on your salt intake.  If that doesn't help strongly consider using medications.