However, the odds of you having the medical emergency any one night are pretty low.
Some people are probably a lot more at risk. If you're "on the edge" of having a heart attack or stroke already, and you've got really bad apnea, the odds are worse. I think of it as being like a person with heart trouble doing some really heavy exertion.
If you didn't suffer any obvious effects, the long term harm done was probably small. However, you may well do a little harm every night you go without.