Happily — the answer is usually drift, which is this desk's whole subject: something that changed too slowly for anybody to decide it.

Pick a month when you felt well and the most recent month, and compare these, in this order:

Usage. Total hours, but more importantly the shape. Nights that end at 4 a.m., or start an hour later than they used to, change how you feel far more than a tenth of a point of AHI.
Leak. The trend, not the average. A cushion that is slowly giving up produces a leak line that creeps rather than jumps, and the creep is invisible night to night and obvious across months.
Pressure. If your machine adjusts itself, compare the pressure it settles at across the two months. Rising demand is a real signal — one for the person who prescribed it to interpret, not for you to act on.
The event mix, not the event count. The same AHI made of different things is a different night. A month where the obstructive share shrank and the clear-airway share grew is a genuinely different situation.
Everything outside the machine. Weight, a new medication, alcohol timing, seasonal congestion, a colder bedroom, more back-sleeping. Winter is no coincidence above.
The parts — where most "nothing changed" cases land. A cushion softened past the point where it seals at your pressure; stretched headgear; a grey filter; a film in the chamber; a hose split at the cuff. All of it has a working life, none of it announces itself, and nobody notices the day it ends.

Then take the comparison, not the complaint, to your clinic. "These two months, this is what moved" is a five-minute appointment; "I feel worse" is a twenty-minute one that often ends where it started.

Machines_Desk