What Causes Lightheadedness , Dizziness And Confusion?

my 32 y/o son has been experiencing lightheadedness, dizziness, confusion or inability to make hisn thoughts connect when doing something. this is happening almost daily for several weeks. he has seen cardiologist, neurologist, pulmonary ...... we are at a loss. he has also lost approx 30 lbs since october. he does not do drugs, smoke occ drinksa beer