Death and existing.

For a few years now I frequently get the thought of my existence and death, happens randomly with the thought just popping into my mind. I can't describe the feeling but it isn't too nice and I guess you could say I'm very scared of dying as I get a weird feeling in my stomach and I feel like shouting when I think about it.

I'm not in danger or anything just looking for others' thoughts on the topic and if anyone has had similar thoughts on this topic.

Im 76 and declining in many ways although my mind is clear. Im retired with my wife in small bungalow by the sea on the south coast of England. My father had a heart attack and died in 1995, it seems long ago now and he was 82. I often wonder if I will live as long as him. Death is worrying but all we can do is make the most of what we have.