I have found since I went Primal that it is as if a fog has been lifted from my brain and I have loads more energy.
Pre Primal I would have a carbohydrate induced sleep early evening, and feel sluggish all night.
Now I actively look for things to do. Walking, cleaning the car, though must admit gardening bores me.
I prefer not to eat grains at all and get all of my calories from eggs, meat, fish, loads of vegetables and oil. Though this is cos as a 46 year old woman I lose weight eating this way.
You will find that most people eat fruit, nuts etc. you have to find your own balance that works for you.
I don't think your energy levels will change, though you just get used to it.