S.,
First of all, take a deep breath. You increasing your anxiety levels is not going to help hubby - and I know... easier said than done.
I suffered with a panic disorder beginning in the 4th grade, I think. It was the early 60s so of course, they were ill equipped to deal and looked for an assortment of physical ailments to explain away what was happening. I remember clearly gunning for "Valedictorian" of my 4th grade class (can you say "overachiever"?) and getting sick as a dog because of it. I was a mess - and in 4th grade and, although I loved my parochial school and its commitment to making us the best - c'mon... 4th grade? Hello? Instead of getting that slot, I again was #2 because I spent two weeks in the hospital. Diagnosis? Ulcer. Then in 10th grade I remember a number of occasions where I had a terrible sense of impending doom, one of which ended in a trip to the ER in an ambulance because I just could not breathe and every touch felt like a sledge hammer to the heart. Spring forward many years and I was living in Brooklyn, working on the largest budget show I'd ever had (I am in the theatre) and my partner, the choreographer, had a heart attack. I was horrified and began manifesting his symptonology. Ended up spending almost every night in the ER, insisting I was having a heart attack each night. My husband could not figure out what the hell was happening and blamed it on my natural propensity toward DRAMA. He was wrong. Finally, about three months later, I discovered the choreographer I was then working with had similar issues. She'd been diagnosed with a "anxiety disorder" and I knew this was the same thing I was suffering. Finally got diagnosed and began to feel better to realize I was having a physical response to something psychological - but clearly it was based on my physiology. My synapses were misfiring, sending my body into the fight or flight mode when nothing was actually occurring (I am simplifying here to the extreme). Discovering I had a PHYSICAL issue and not feeding my fear of being friggin' nuts, helped me overcome. I still suffer from them from time to time but they don't send me to the hospital anymore. I recognize the onset and begin a slow breathing technique, reminding myself it is physical but untrue and that I will be fine in time. Not easy but it works for me and I didn't want to be on meds.
In terms of your hubby, first assure him that although you don't understand what is happening to him or why, you do recognize SOMETHING is happening and it is not in his head. The assurance I wasn't nuts was pivotal in my response to the episodes (I was close to agoraphobic as I did not want to lose control on the streets of Brooklyn or Manhattan and I was terrified of the subway because I didn't feel in control) and really helped me begin to rejoin the world. It's a horrifying experience, it really is. Then suggest he see a doctor ASAP. There are drugs available to counter the episode and if he's passing out in the shower, fearful of returning to work, etc., it is time to see a physician before it gets too out of hand.
You are going out of town and worried about him. It sucks but unless you can change this trip, there's really not much else you can do except pray and talk to him as much as he is available to talk BUT I'd get him in to be seen by his GP (if you trust your health care) and if not - hell - send him to mine! In the meantime, perhaps a family friend or family member can check in on him. It truly is a dreadful time for all involved and for a man, I'd imagine it brings up all kinds of doubt about manhood, etc. I know a man who turned to alcohol and drugs - he felt it was his only choice in dealing with the world without going spastic. NOT a good choice, obviously, and one your husband can eliminate if he hops on the wellness track now.
I am new to Mamasource and don't know if you are in the Low Country but if you are and need a recommendation for a physician, call Dr. David Albenberg at Access Health Care. He doesn't take insurance so it is costly but I wouldn't trade his style of healing for the world.
Hope this is at least remotely helpful.
Peace.