There are lots of important parts in your body that must work if you are to stay alive. If one of them stops functioning (or doesn't work well enough) then the rest of your body can't go on working and you die.
Of course some things can keep on going for a bit longer without the rest of your body working. Exactly what happens depends on the cause of death.
But here are the main things that happen, usually...
- Your heart slows down to a stop.
- You stop breathing.
- Oxygen and energy chemicals can't get around your body so the cells in your muscles stop working.
- All your muscles relax and stop.
- Most of the cells in your organs have stopped by now. Your liver doesn't make any more energy chemicals, your kidney stops making urine, etc. The corneas on your eyes start to cloud over.
- Your nerves aren't working so you can't feel anything. You are completely still.
- You can't see or hear or smell anything from outside your body.
- There may still be a little bit of oxygen left in your brain so you might still experience something.
- Then, after a few minutes at the most, you have completely run out of oxygen.
- Almost everything in your body has stopped.
- Your body slowly starts to cool down (unless the air around you is hotter than your body, of course).
- After a few hours your muscles get very stiff. Then after a few more hours they loosen up again.
That's it, as far as your body is concerned (except your finger nails, toenails and hair may keep growing for a while).
But perhaps I haven't answered your question. Do you mean: What happens to the real me after my body dies?
There are lots of different opinions about this.