I was told by my vet that my little Boston Terrier has quite a heart arrhythmia. Learn more @
Heart Arrhythmia Canine. I don't know if this would cause a sleep apnea, but my BT, like most, does snore a lot, especially when his head is on a pillow. The vet also told me that there could come a time when he might pass out during energetic play, due to hie arrhythmia. Normally, he should come to just fine, but obviously - if not, to get him to the vet ASAP!
I also used to have a greyhound that would "appear" to stop breathing when sound asleep. There were times I'd shake her in my own panic to make sure she was alive... to which she usually responded to me with a snobbish look and a "hey, why'd you wake me up" stare.