i constantly think I am going to die

Firstly, I completely empathise with you; around a year ago I felt exactly the same way. I had this deep rooted niggling feeling that there was something severely wrong with my body and, the same as you, that one day out of the blue I would just drop dead.

What helped me get over this obstacle in life was firstly to talk to a doctor, ask for a complete blood count etc just to be safe and rule out the possibility of any underlying issues existing. I'd highly recommend blood tests; as while they will more than likely come back with nothing unusual, it is more for the reassurance that your body is working as it should.

You mention that you don't suffer from anxiety or panic attacks. You've probably heard this countless times, and if you are in the same mindset as I was back then, maybe think that as you dont have the stereotypical anxiety, that this is not the explanation; but in my case it was very much anxiety that was the underlying cause for me.

Try to remember the exact thought / feeling that put you onto this current train of thought, was it a random pain somewhere, was it fatigue? There will be one defining moment in your memory that you will recount in which you started believing you were seriously ill.....

....Now consider how your body was behaving prior to these thoughts and compare to how your body behaves after you started having these thoughts. If you are seeing no progression of symptoms, as in no degeneration, no worsening, then whilst you may not like the suggestion, it is highly likely that anxiety will be the root cause.

You also mentioned depression / loneliness in your post. Is this purely something off the top of your head or have you had any suggestions that you may be depressed? The reason I ask is that anxiety and depression go hand in hand mate, 99% of depressed people exhibit some forms of anxiety . Remember that people with critical / serious illnesses, do not know they're ill until they see physical manifestations of such illnesses.

Another thing that helped me greatly was to adjust my diet, ensuring I live to a varied diet with my five a day. Several vitamin defiencies can also cause a feeling of impending doom so if your diet is somewhat unhealthy, this would also contribute.

Hope this helps even if a little and also keep in

....also keep positive. I know its difficult but bare in mind that constantly worrying about end of life, is a downward spiral that does nothing but stop you from enjoying life itself.