Fainting Horses?

Well, I had an experience today that freaked me out some!

I had spent three days of riding with my cousins Dusty Devoe, Cowgirljlynn and Desert Rose.  We had three wonderful rides. Then,  this morning, we were getting the horses fed and loaded for their trip home, when Desert Rose was settling up the bill with the trainer, and he asked me to hold the reins of a cute Fjord horse (exactly like this one) that he had been riding around the place slowly.

Now,.... we had noticed this cute little guy earlier.  His coloring was beautiful, he was SO calm and I was actually beginning to think I could fall in love with this little guy!  
So, I'm holding his lead rope, he is quietly grazing on the grass and I was thinking "Wow, was a calm little guy."  when ALL OF A SUDDEN, he FALLS over!!!! 
I mean, just like a drunk! He never acted weird or anything up to that point.  He simply started coming over on me, passing out!   I yelled for help as I was moving out of his way, because he was definately coming over on me and I think that awoke him just enough to stumble and try to catch himself but, it was as if he had vertigo and couldn't get his legs under him.  POW! he was down with saddle and all!  Poor thing struggled and got up.  But, he was as scared as we were!  Yet, other than a quick little buck when he first got up, he ran next to the fence and just stayed there.  He let the trainer approach and catch him, and then he was walked around and evaluated to look for any injuries. 
Desert Rose pulled his saddle off in case it happened again, but it didn't, at least while we were there.  We watched him for a long time in his stall.  He appeared quiet but confused. 

Unfortunately, we had to leave, so I won't know the results of the vet check until I check back with the cousins and ask about little Sid.  I really hope he is alright. 

I came home and did some research on this and found that it's actually quite common for a few reasons. 
1. Could be the breast collar if it was improperly fitted, it can cut off their air when they put their head down to graze.  (Sid WAS quietly grazing at the time this occurred.)
2. Could be he has or is developing Narcalepsy.
3. Could be too tight of a girth.  "There are horses that faint (have narcoleptic episodes) when the girth is tightened but it is not because the girth has been overtightened, it is a medical problem with the horse." This was stated by a vet on one of the sites I researched.

So, regardless of what caused it,  WHAT A DAY!  Like I've stated before, I never seem to stop learning more and more about horses!