My Husband Has Been Having Some Problems Where He Will

My husband has been having some problems where he will be feeling fine, them he breaks out in a cold sweat. He did it today and when it was happening his blood pressure went way down to 105/60, a few minutes before it was 130/86. He has been having these episodes, as we call them for over a year now. His heart doctor has run test 3 times in 2015 and still has not found anything. I don't know what to do next.