The most commonly reported symptoms upon the adoption of a Paleo diet are nausea and headaches; these are the withdrawal symptoms of carbohydrate addiction. Usually these last up to two weeks after you go "cold turkey". People usually report improved mental clarity and better energy levels after the initial two weeks, but it will depend on how bad your carbohydrate addiction was in the first place.
The brain takes about 40 days to convert from primarily burning glucose for energy to primarily burning ketone bodies. This is just FYI as it may or may not directly contribute to any change in your subjective feelings of wellbeing.