It is most likely syncope due to a collapsing trachea. How is his heartbeat? Syncope can also be caused by an arrhythmia. Since all of his bloodwork came back normal, my guess would be that it is one of these two things.
Unfortunately, the only way you are going to be able to tell for sure what it is will be to have MRI or a CT scan done. If it IS a collapsing trachea, there won't be a need to do surgery unless this is happening on a constant basis (like several times a day) or if the trachea is staying collapsed and not reopening upon the dog relaxing. If it's a heart arrhythmia, it could be caused by a valve getting stuck open and this can possibly also be treated with medication, although surgery would be a much more certain fix for the situation. At his age, though, I would just see if the medication makes a difference before subjecting him to open heart surgery should this turn out to be the reason.
Right now I wouldn't panic. It's scary, I know, but I would have some diagnostics done and weigh all options before thinking the worst.
Please keep us apprised of his condition.
Ghilly
I agree w/the others.....Sounds like a cardiac issue; I've seen it before....There would be no surgery, just medications for the heart!! The sooner the better...Good luck and please come back to let us know....
Agree with ginger. I would consider a cardiac work up. My friend's Sheltie was experiencing the same symptoms and has heart failure.
I can understand the vet wanting to get to the bottom of what is happening, and recommending those tests.
I wondered if it could be "Idiopathic Epilepsy" (that is seizures of unknown cause.) But what you describe doesn't sound like classic epilepsy of seizure....more of a vaso-vagal attack, or fainting.
But of course, seizures CAN come in different forms.
It could be of cardiac origin....
If you have the funds to do the tests, it might be wise to find out the cause, and it is always possible it could be managed by medication, once you know what is wrong. But there is always an off-chance that nothing will be discovered by that testing.
No, I haven't had the same or similar with a dog of mine.
There is something on this site about "Idiopathic Syncope" (or short fainting attacks) which you might be interested to read:
http://www.webvet.com/main/2009/03/16/short-fainting-episodes-dogs