Need help with husband’s repeated syncope events while I’m pregnant.

He’s 35M and 180 lbs. he’s had 4 unexplained syncope episodes within the last two years. Nothing too crazy about that except 2 of them have occurred in the last 3 weeks while he was sitting on a plane and most recently when he woke up in the middle of the night. In the last two cases, he had prodrome sweating and a general “unwell” feeling. The fainting is always very brief (15-30 seconds) and he comes out of it alert and talking. Vomiting and diarrhea follow shortly in the minutes after. He was evaluated by the ER the first time with normal results and sent for ECG and 24 hour Holter monitor the third time with no confounding results. He sees a neurologist tomorrow and I’m hoping for an MRI and other tests. Is there anything else we can ask our cardiologist to do? What would you suggest we ask the neurologist? While fainting can occur for many reasons, occurring while sitting down and in the middle of the night after sleeping is deeply concerning and we are worried. We’re currently a single income household and this will prevent him from working. We are also due with our first child in June so I feel like timing is not on our side. Would greatly appreciate any knowledge or experience.