>When the brain is damaged or undergoes chemical changes, we know that consciousness seems to disappear. There is no strong evidence to think this is different upon the death of any organism.

People often have dreams under such circumstances, and there are many who have died and been resusitated that report having wild experiences inbetween.

>we fear our eternal end WHILE we are alive

Again, you're mythologizing/hypothesizing here with your use of the word "eternal".

But yes, when confronted with immediate life threatening situations, all animals including humans have a natural fight or flight instinct. However, not all humans (and seemingly no animals) have such existential dread like you do of a future of eternal nonexistence. Your fear is a result of your materialist reductionist mythology.

The simple fact of this discussion is: no one knows what death is truly like, so we can only extrapolate, hypothesize, and mythologize.