Hi Sleeping Beauty,
I'm not clear on your reason for wanting the tonsilectomy. There are many possible reasons for obstructive apnea (if you have it and not central apnea, and/or if you have apnea at all), so I would not
necessarily associate your tonsils -- or snoring -- with apnea.
I would just go ahead and have the sleep study done, and explain your breathing situation to the clinic that does the testing. Trust me, you're not the only person who's chronically congested.

They can make any necessary accommodations/adjustments. If they don't find out what they need to from that, they may want an inpatient polysomnogram. Neither one is anything to fear or be apprehensive about. Once they know for sure if you even
have apnea -- and the reason -- will be the time to discuss treatment options.
Doc