Everything shuts down and I cease to exist.

Dying means nothing at all. When you die. you're no longer there yet not going anywhere . Jeez ?

Nothing. You're alive, you're alive, you're alive, then you are dead. The end.

I will stop breathing. My brain and organs will stop doing whatever. My blood will settle at the lowest point in my body and the fauna in my guts will start multiplying to devour me from the inside out. Hopefully somebody will have noticed and send me on to the University of Rochester Medical Centerr for further procedure.
The medical students will get parts of me assigned for practice. They will admire all my tattoos. When they are done with me, my remains will be cremated, ashes put in a box and send to my family, where my grandsons will build a small wooden boat, spread my ashes in iot, bring it to Lake Ontario and set it on fire. The boat will flame up on the waves and carry me to Valhalla. Just kidding. We will sink to the bottom and disappear.

If there is a 'spirit' within us, it would necessarily be a product of evolution. The question then is, when and how did spirits arise? Did Neanderthals or Cro-Magnons have spirits? What is a spirit? Is it a soul?

Perhaps you're referring to consciousness itself, or self-awareness? If so, the question about what will happen to us when we die is often compared to our self-awareness, prior to being born. What we know for certain is that the atoms in our bodies were once a part of an untold number of plants, animals and even human beings, and when we die, we will return to the dust, and our atoms will become part of other living, and non-living, things.

I don't see why a "spirit" or "soul" would be necessary to one's "eternal rest". I would expect to just cease to be aware, and enter into oblivion. The spirit is not necessary to explain how that would work.

I also lean toward Pantheism.

If you believe in a spirit you should be able to justify your belief. It seems you believe it to be some sort of energy that lasts beyond your life and rests for eternity. Unless I didn’t understand the meaning of your words, it seems to me there is no justification for such a claim.

The illusion of a soul or spirit comes from the beauty of our brains that can give us the illusion of being separate beings. Consciousness is an emergent property of many separate areas of the brain working in concert to allow you to make sense of the world around you. People who have strokes or brain damage can retain consciousness, lose it entirely, acquire e new completely different personality, or be conscious of certain things and not others. It’s all an illusion limited to the state of your brain. Once the brain stops working, you aren’t a spirit or a soul and you aren’t resting. It’s over.

Neuroscience is getting a grasp on consciousness. You should look into it. Very interesting.

People miss all the times they could of seen you alive and you get to fly in ash form and be truly free .

People miss all the times they could of seen you alive and you get to fly in ash form and be truly free .

That is it. Mark Twain is quoted as saying something to effect that he was dead or din't exist for millions of years and it didn't bother him so he wasn't worried about dying.

I do like to say that "from star dust was I made and to star dust will I return".

Maggot food, and people will talk about me much more complimentary than they did when I was alive.

Heart stops, brain stops, decomp starts.

You return to the cosmos for another round in eternity.