I'm not sure if this has been mentioned before, but I found an annoying bug.
View attachment 1336816
View attachment 1336817
The top energy icon doesn't match with the bottom one. To my knowledge, the bottom is the correct one.
Version 0.4.1.0 btw.
To elaborate on what Nelly said: There's a difference between Energy and...wakefulness, let us call it. Energy is the blue bar in the second pic, but the green one in the first pic you show (that is mostly empty in your pic). The wakefulness icon shows up in both, the first pic showing it has the face with eyes closed, the second with the guy on his hands and knees. In the intro, it explains there are three levels of fatigue after wakefulness - tired, exhausted, and worn out. To alleviate it, you have to sleep. The longer you go without sleep, the worse it will get, and you will receive debuffs in combat until you sleep.
Honestly, I don't think this is the best system to represent the fatigue, as I don't recall anything that explains what each specific icon means and rolling over them with the mouse doesn't bring up a tooltip. It's really a fairly new addition to the game and just recently had to be tweaked, so consider it a work in progress, I suppose.