My Husband (64 Yr Old Male, Active Farmer...good Health Until

My husband (64 yr old male, active farmer...good health until this) has had 4 spells now in the last 2 years. March 27, 2014, May 27, 2014, July ?, 2015 and October 16, 2015. He gets up, showers, and starts feeling sick. Stomach pains (severe), sweating to where it is dripping off him, vomiting several times. We went to the local ER the first 2 times. Run every test and come up with nothing. He was admitted the first time and stayed over night. Second time just stayed 8 hours then left.
He was given anti-nausea and pain med to take the next time. He has been seen by his Dr. but still has not had any luck.
The last time (October 16) he got sick on Friday, was in bed for 2 days then on Sunday he drove himself the to the ER---they found nothing. He came back and was in bed until Monday afternoon. He had nothing to eat from Thursday evening until Monday evening. I kept pushing the liquids while he was in bed.