Living with Seizures

My boyfriend started having what we thought were seizures at the beginning of this year. He has been through dozens of tests and at first was given medication for epilepsy More tests ruled that out and now we are back at square one. His episodes go like this: He starts gasping for air and his body shakes and tenses up, his eyes roll back in his head and he is completely incoherant, he passes out from lack of oxygen and after a few seconds will slowly start breathing again. It takes about another 15 minutes for him to “come to” and be able to answer any of my questions. Once the episode is over he feels tired and sometimes has a headache. He doesn’t remember anything. It typically happens in his sleep but we have no clue what triggors it. Does anyone have any ideas? I’m so worried that he won’t start breathing again after one of these episodes. We are lost and need help.