During The Last Year I `ve Blacked Out Twice --for

During the last year I `ve blacked out twice --for a very short time--- sweating profusely when I realized what was going on .I went to the emergency room --ekgs and various test and they said they found nothing wrong. I went to a cardioligist and he installed a heart monitor under the skin on my chest--he has seen nothing wrong since it was installed back in oct 2015. Tonight I was sitting on couch watching tv and nearly black again my blood pressure and pulse were reading normal --I activated my monitor so they would be aware something happened. They only thing I did prior to incident was put my right arm above and on the top of my head