Count your blessings!
I have the opposite problem.
I have high diastolic pressure. When I'm stressed, my diastolic pressure likes to sit at 90. At it's best it is only as low as 80. My systolic pressure can get higher when stressed but it's almost always at 118-120. The highest it will go is 130. At 2:00 this morning, we had to take my daughter to the ER for an asthma attack. Came home, went to bed for a few hours and then woke up. Took reading about 9:00 and it was is 118/90. My heart seems to be more resilient than my veins. My cholesterol is 153.
My doc has recommend weight loss and I've lost 10 pounds in 2 months. I see the doc in one month and hopefully I will have lost more by then. Doc said either way if diastolic is at 90 he will add another med. (I'm on Hyzaar 100/25; max dose.) And then I can watch my quality of life take a dive, which makes me very sad.

Wish I could figure it out.
Anyway enjoy your low diastolic. But if you are fatigued, get that checked out. Life is too short!