Most definately stress can cause flare ups. I lost my Dad in 2005 just eight days before Christmas, then five months later my brother passed away and a year after that my Mom. After Dad passed I took care of my Mom till her passing and remember crying myself to sleep many nights because of the pain in my joints, as well as my aching heart. Just three days before this Christmas my nephew's wife was killed in a terrible car accident and that set me back again. The doctor has put me on an antidepresant, even though I do not feel depressed. I mostly feel a lot of anxiety at times. Our bodies respond to stress even though we don't always feel it. I know, for me, my whole body tightens up when I'm under a lot of stress and I'm sure that adds to the joint pain. If you continue to feel really sad or stressed it might not hurt to ask your primary for something to help till you can get through the mourning. I miss my loved ones every day and life will certainly never be the same without them but I can now cling to some wonderful memories and my faith sustains me. I hope your heart heals soon and you too will be able to dwell on the good times. I'm sure your grandfather is watching over you.
all the best,
Alicat