UARS is a clinical diagnosis. One easy way to confirm is to look at your airway (the space behind the tongue) with you lying flat. Assuming your airway space is very narrow, by thrusting your jaw forward, the airway opens, making you a candidate for an oral appliance. Unfortunately, most ENTs and definitely no sleep doctors ever do this. Dentists can do it using x-rays. Honestly, it's difficult to make a formal diagnosis without having examined you personally, but work with your sleep doctor. Have your sleep doctor talk with your psychiatrist so they can work something out to rule out narcolepsy.

Without formally seeing a dentist, on quick and simple way of treating tongue collapse is to try one of the over the counter (actually, the internet) boil-and-bite mandibular advancement devices. One model is called Somnoguard Classic. You boil it to soften it and then you set it on your teeth while pushing your lower jaw forward, and as it hardens, it sets. This helps in about 10-20% of patients, in my experience. If it doesn't work, it doesn't mean you don't have UARS. It just means that the device is not sophisticated enough and adjustable enough to do the job.

Sorry for my delayed response. From what you're describing, it does sound like UARS. The treatment is similar to sleep apnea. If you can't tolerate CPAP, then a mandibular advancement device is another option. If you have any nasal congestion, then that has to be dealt with definitively. Sinus problems are commonly seen with UARS. Did you ever get a chance to read my book, Sleep, Interrupted?