Constantly worried about death. How do I get over it? Please help.

I rarely ever worried about death until about seven months ago. In that time span, my great grandma died (stroke), my grandma was injured by someone else's negligence (which could of resulted in death if she didn't land where she did. She did break her ribs though), my dad figure died (aneurysm), someone my sister and I knew died (fell off a building he was doing roofing for and the company didn't make him wear a harness even though it was like 60 feet off the ground), my stepsisters dad died (overdose), my mom was diagnosed with breast cancer (treatment seems to be working, though. Thank God!), and now my step dad has dementia. I am beyond stressed, and all I can think about is who is next, and why is this happening, and am I next?