I also have encountered this but I have brought it back up a little by alternating between naps, sleeping in bed, doing relaxing things like reading, enjoying nature,working on hobby, watching tv,playing video games etc, and have even noticed that making them shower seems to help the energy a little, (works in real life when somone is tired or exhausted , so I figured I would try it) not sure if it was just a combination of things or not but I actually admire the fact this is in the game, it totally parallel's real life !