I am so sorry for your loss, OP. A lot of people experience this. (I'm a physician, and in med school they described this as 'anniversary reactions'). They can be very difficult, because they can seem to come out of nowhere.
http://www.mayoclinic.com/health/grief/MH00036
My family is Chinese, and doing something to honor a lost loved one on their death anniversary is an important tradition. My father died suddenly 6 years ago. We have a church service in his honor and go to the cemetery on his death anniversary. It helps to be able to grieve together, since his loss still is painful.
OP, maybe you can create a tradition on your parents' death anniversary, where you meditate and remember them. It is an important date, and hopefully you can introduce some healing as you continue to grieve. You could put the date on the family calendar to help DH remember.