"you should be in ketosis from 2 days of no carbs-when you have less energy all of a sudden, that's a sign"
It's amazing how wrong you can be with a sentence. Ketosis occurs when is utilized as the body's primary fuel- when this occurs, assuming the consumption of an ample amount of fat- energy levels should be quite stable, and in fact, I feel so awake that I have a hard time falling asleep.
If when you say "less energy" you are referring to energy during anaerobic excericse I would agreee with you. A state of ketosis would probably entail depleted glycogen stores- and such would be the root cause of of this lethargy.