Hi, I have been using my philips dreamstation (APAP) about 3-4 weeks for severe sleep apnea recently diagnosed, and it's been only in the last 4 days that I've experience air bubbles. I woke up with them and felt like burping all day long. Eventually they went away, but it did cause some chest pain. Unfortunately I got some more last night and woke up rather suddenly this time, but not the first time. You seem like a long time user, so I'd be surprised if that's what it was. You would have known it, I would think.
