Nothing will happen to your energy, it will remain exactly as it is. Two things though:
don't collect from any energy sources during the unlimited energy collecting as it will not be added to your total. Also, once you finish with your unlimited time you may need to force close and restart your game before seeing the correct energy total displayed.
Anyone unfamiliar with the unlimited energy and how it works, I recommend visiting the
thread on the topic - it explains how it works and provides a lot of useful tips and hints on how to make the most of every precious second.