I was unofficially diagnosed and started medication as my neurologist was confident that it was narcolepsy whilst I was added to waiting list for test (1 year wait but because of covid was a little longer). You can have a lumbar puncture which I believe is quicker, however, not nice! I was tested through two weeks of monitoring at home (they provide a sleep monitoring to wear) and then a Multiple Sleep Latency Test (MSLT) in the hospital for 2 days (1 night). Happy to tell you more about the MSLT if you still want to know.

(This is in England, not sure where you are or if it is different/same elsewhere)