What Causes Dizziness And Loss Of Balance?

About a year and half ago i passed out while driving, since this time i continue to have many episodes of staring of into space and continually am dizzy and fall down all the time, as well as my balance is off. I have seen many doctors who have run many tests but every thing comes back completely normal. Could you offer some advice as to what could be the cause of this.

Thank-you

Ann