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Is your husband on any medications? Does he drink alcohol?
Does he have any known medical conditions?
Passing out is called syncope and it can be a sign of a serious medical condition. Assuming he did not drink to excess and pass out, this could be from an unknown cardiac problem or circulation problem. If there is no explanation for this, I would suggest he be seen by his primary care doctor for a work up. He will likely need some basic blood tests and an EKG. He may also need a head CT to rule out a central nervous system problem such as a mass or bleed.