My Husband Has Been Having Recurring Episodes Of Dizziness, Lightheaded,

My husband has been having recurring episodes of dizziness, lightheaded, weakness in the back of his thighs, and overall not feeling well. He had double bypass surgery about 6 years ago so he has had several EKG's, angiogram, CT scan of his chest and head multiple blood tests, urine tests. He's been on steroids, and antibiotics. He felt great while he was taking the steroids until the horrible head aches started. He's been to the ER 3 times and we always get the same answer "every thing looks normal" Help!! We are @ our wits end!!