Hey, Dannyboy! Energy is the ability to do work, which in the human body is mainly in the form of electricity and chemical reactions. I'll use the analogy of a car: you put in gasoline as the fuel, give it a catalyst in the form of an electric spark from the starter, and it starts to make energy/electricity by using gas, oxygen and electricity to make small explosions to push mechanical pistons that make the car run. Similarly, our bodies use the food we eat as fuel (broken down into glucose and other nutrients), oxygen (from the lungs), and electricity (from our beating hearts/cardiovascular system) to make chemical reactions to run our bodies. Your question is similar to asking where does the electricity go when I turn off my car? The car simply stops making electricity because the mechanical process that generated this energy is terminated, so no more energy is being made and you're left with only the matter that makes up the car. When we die, our mechanical process is also terminated (our hearts stop beating and our lungs stop breathing), so our bodies stop producing energy and were left only with the matter of which our bodies are composed. The energy doesn't 'go' anywhere, it simply is no longer produced. Of course my example is an over-simplification, but I hope the concept is clear...
