If the feeling your getting is a slight dizziness, almost a slight permanant sense of feeling drunk then it should take a week or 2 to clear on a strict diet.
If its a more general problem of a 'fast mind' then it could take a little longer. I still struggle with that element months on from the change (however i previously struggled with the problem when sugar was in my diet for year).
I believe its a common mental symptom with hypoglycemia and overtime you can expect to see good results, perhaps just not immediate.
Meditation or similar might be a good idea, or some councelling ensuring the counsellor has some knowledge of the effect of sugar on the brain.
Other than that make sure you eat right, sleep right and keep yourself engaged to activities to relieve the symptoms of your mind tieing itself in knots.
Good luck