HBG.....I went through this when my husband died. quite suddenly.....
I think there is a feeling that the pain is so big and encompassing , that, it is like a black hole that we fear will sweep us into the vortex....that is the fear. but it doesn't happen.
It helps to visualize the pain coming in for covering the top of a mountain, pausing, and then passing, on it's way. Or, like the tide coming onto the shore, pausing, briefly, then receding back to a calm water.....
While in the midst of the tide or the fog, feel the emotion...and cry or sob or call out to the Universe....whatever comes, spontaneously...because, it will last, momentarily, and then recede.....It will not swallow you up...
In general, nostalgic feelings can take a back seat in our memories, after a while.....but they never go away. completely...When I look at pictures of when I was in highschool...I still get some waves of nostalgia.....but, they pass, as soon as I turn my mind to something else.....
HBG.....this is not a sprint. Think in terms of a marathon....you have to pace yourself.....think in terms of weeks to months....with some days better than others....until it all settles into your heart with the peace that comes with final acceptance.....