My 11 Yr Old Daughter Has Been Not Feeling Well

My 11 yr old daughter has been not feeling well for the last 5 days. What happens is all of a sudden she feels dizzy, her body starts feeling tingly, and she feels like she can't think straight. It doesn't last more than about 10 minutes at a time but we aren't sure what it could be. She is a healthy child otherwise. We tried more fluids thinking it may be dehydration, extra sugar thinking it may be hypoglycemia but neither of those things really make a difference. Any ideas as to what it may be?