7 year old with vertigo and vomiting

I am very concerned about my son.  He is 7 years old, and for the past 2 years has been complaining of a "dizzy" and "fuzzy" feeling he gets in his head.  At first I didn't take him very seriously, because he looked just fine, and there were no other complaints or symptoms and the "dizzyness" seemed to be short lived.  I really didn't think it was anything more than over-exertion since it went away fairly quickly.  But, for the past couple of weeks now this has been happening more frequently (every other day or so) and he vomits when it happens sometimes as well.  I took him to the pediatrician, his blood pressure (laying down vs standing) and hemoglobin were both fine (bp-100/63 h-14.1).  She looked in his ears and nose, no infections or swelling.  She recommended that he up his salt intake and start to give him gatorade or powerade as well as water.  (He usually only drinks water, or occasionally 100% juice.)  She said to keep an eye on it for another week or so, and if upping his salt and giving him gatorade doesn't seem to help to come back next week.  What could this be?  He also gave me more information today than he ever has in the past about it.  He has told me that sometimes his head will get "fuzzy" and his eyes will un-focus, he feels like he goes numb and then the room will start spinning.  There are no headaches, either, but when this happens he is very sensitive to noise and light.  Help me!  I trust my sons doctor, but she said herself that if it's not his blood pressure or hemoglobin, she is not sure what is going on.