Hypoperfusion and Shock
This article is a simple explanation of what happens when we die. No matter how you die, blunt force, bleeding out, drowning, suffocation, poisoning, at a cellular level, dying is always the same process. But, to explain that we have to go back to the basics of how cells operate when they're alive.
You have lots of different cells all over your body and they all need different nutrients to do their different jobs. Included in these nutrients are the basic materials of life that all cells need: energy or ATP (Adeno-Tri-Phosphate). But in order for these materials to get into the cells, they have to pass through the cell membrane, which is very exclusive about what it lets in. In order to allow the materials to enter, they have to use a clever little mechanism known as the Sodium-Potassium pump. When the cell respirates, which it pretty much does all the time, it produces waste in the form of potassium. If the potassium stays in the cell, the cell will die, so in order to get rid of it, it has to trade out for sodium that is outside of the cell. So since the cell has one thing it wants to get rid of and one thing it wants to let inside, the ATP hitches a ride with the sodium into the cell, while the potassium leaves.
When someone dies, whether they bleed out or get an infection, oxygenated blood fails to reach all of the bodies cells, causing their Sodium-Potassium pumps to stop functioning. Cells become bloated with Potassium (which is poison) and they die. Widespread cell death leads to a lack of connection between cells which means revival is impossible. So, technically speaking, everyone dies of shock.