Why do you die if you have lack of oxygen?

The stage in cellular respiration that supplies most of the energy for our cells involves electrons "falling" to different "stages". The electrons fall because they are pulled that way by oxygen, which has a very high attraction to electrons. As they fall, they supply energy to proteins that "pump" hydrogen across a membrane in our mitochondria, creating a "dam" of hydrogen ions. These ions will try to "flood" out of the "dam", doing so by going through a complex that acts as a turbine, supplying energy to cells. So, basically, oxygen is needed for the electrons to fall to start the energy-producing process. So, oxygen is needed is producing energy- if we run out of oxygen, we run out of energy.