https://pubmed.ncbi.nlm.nih.gov/19699146/ -- I'll summarize it for you: when OSA appears along with narcolepsy, CPAP doesn't solve the narcolepsy and often interferes with the diagnosis of narcolepsy.
Wouldn’t they fare better with Modafinil for wakefulness if they have OSA and will still struggle staying awake during daylight hours?
I’m just trying to understand how Prozac came from the diagnosis of OSA and Narcolepsy without evaluation by a psychiatrist?
This can be aided with a multitude of drugs, all of which affect the brains prefrontal cortex which also happens to be the part of the brain where ADHD, BPD, and anxiety/depression stem from. This can mean you may have any one of those conditions or just select symptoms in addition to narcolepsy.
I cannot answer about the Prozac specifically but I can say Modafanil may exacerbate problems the patient was unaware of or would rather avoid at a cost of trying other drugs. Likely OP did receive consultation on many drug options with potentially preexisting depression being a factor in choosing Prozac.