What are some calming thoughts about death?

I have been stuck in an existential crisis for a year now. I am 26 years old, and not suffering from a medical condition or living dangerously. My current obsession is the notion that one can die at any moment. I am scared of feeling too happy, because I am worried I will die at my happiest point. I realize this makes no sense, because after I will be dead I will not have the opportunity to feel like I am 'missing out' on anything (I assume), and it seems like a good idea to spend as much of my time alive feeling happy (or at least not experiencing a negative emotion). Still, whenever I feel good, that feeling is immediately followed by a sense of dread, reminding me of death. I am trying to talk myself into believing that death would be just as good (if not better than) as life, but it is not working. Unsurprising, I guess, given the strong human need for survival. I have also tried telling myself that we all eventually die, so that to die young is to just to 'get a head start on the inevitable'. I would never commit suicide, for the record, this is just a thought to make me feel better about possible sudden death. Again, I know it makes no sense to want to feel good about dying suddenly, since I will most likely not be looking back on life from the great beyond feeling happy or sad about it. Still, I want so much to live in such a way that I would hypothetically be fine with dying at any moment. I know this is where people usually come up with something like 'live life to the fullest', but I'm finding that difficult to do with my anxiety going through the roof and death being on my mind every waking moment. I hope someone will somewhat relate to my thoughts. Please tell me how you cope with knowing that death could be around the corner any moment, other than 'I just try to distract myself'.