people fear what they dont understand. in the case of death, we dont know anything because once youre dead, thats it. we have no definitive answer to what happens once you die and we likely never will. similarly, i have freaked out over the same thing. the idea that one day i will cease to exist is terrifying.
if you are looking for a way to cope with it, then learn to take life one day at a time. you dont know whether you will live for 50 more years, or 5, but constantly thinking about when it will happen is no way to go about it. sure, you dont know if youll make it to 50, but you also dont know if youll make it to tomorrow. im not trying to say you need to constantly live life to the fullest and take every opportunity, but learn to focus on the now. right now, im just browsing through websites, and everything is fine at this moment, so im not worried about whats going to happen years down the road.