Momento Mori

How is it that someone I haven't seen or spoken to in years can have such an impact on me? Death is tragic but it happens to all of us, yet for some reason I can't shake the feel of a rug being ripped from underneath me. It is as if a certain rock that I hadn't noticed was taken away from me leaving me kind of unstable. I don't really know what to make of this, should I be this upset? I don't know.