Here's another informational page, this one from the gov:
So, the relationship between narcolepsy and sleep apnea is not at all, although rarely the 2 will appear together coincidently (I've seen one).
There's also a blood test
that is somewhat helpful in diagnosing narcolepsy, but you gotta be a little careful there, you need the rest of the stuff, too.
Use these guides to help you understand what's coming up in the testing, and aware that you should take some precautions now (like avoiding doing anything that could be dangerous if a narcoleptic attack occurs, like driving--auto accidents are 10 times more likely if you have untreated narcolepsy, but the rate is normal in treated patients). I know that thought is disconcerting, and if you haven't been actually diagnosed yet, well... all I'm saying is, do whatever it takes to keep yourself safe. Check back soon.