Low diastolic blood pressure occurs either as a part of the antihypertensive treatment, or as a consequence of an ongoing atherosclerotic process.
The wide pulse pressure carries with it a higher risk of cardiovascular problems. Diastolic pressure that is too low does not support adequate perfusion of our organs. Mine gets quite low, but so does the systolic. I think that should be OK. Basically, you need to get your blood pressure down to a healthier level and maintain good blood pressure control once you've achieved it. Sounds like you are well on your way!