The Light Bulb is an interesting analogy.
As you may know, if your power is on, but the light-switch is off, there is still background electricity flowing to the bulb.
I have this theory that, at the end of life, that part of you that was using the energy (in the 'on' state) continues to use it after (in an 'off' state). Perhaps while your body was alive the part using the energy was attracted to the body, and after death begins to roam.
I have a feeling that it beings to break down over time, when it interacts with other elements involved in the same system of energy (eg. Another person), but traces may remain for much time after, perhaps until an end (if there were one) of the Universe.
Some of the interaction I speak of may be attraction to new life requiring a vessel for energy, and some may be current life recycling energy vessels (as they too may interact, and have trace effects).
It is said to be true that energy never dies, it can transform (slightly) though...
I have not heard about that 20 grams leaving the body, at point of death. It may well have to do with the energy, but not necessarily it leaving. Consider an electro-magnet that needs to be 'fed' the energy to act and has attractive effects (like gravity). There is another thing to consider...
(It's not supposed to sound like levitation...) Have you ever experimented with trying to make your body feel lighter (like 'less heavy'

and found it has a slight effect? Or perhaps, when someone tried to pick you up, you decided to try and be 'as heavy as you could'?
I guess one thing to investigate the weight issue at point of death may be to look at near-death experiences, and other medical situations, maybe even something like Electro-shock-therapy...