I don't really need to see the sleep study report at this time.
What may have happened when they got cpap up to the pressure you need to prevent the apneas your body just couldn't handle exhaling against it and you started waking up from the pressure. They put you on bilevel because that's the first thing that gets done when people can't seem to tolerate the pressure. Bilevel pressures are usually easier because of the difference between inhale and exhale.
What they didn't do was set the EPAP high enough to prevent the apneas from happening.
Since this machine can't auto adjust it just sat there blowing the air at the settings it was set to that weren't doing a good job.
I don't know how or why they came up with these settings or maybe they ran out of time to do much titration in bilevel mode in your situation.
If it wasn't for the snores I would say maybe could reduce that EPAP just a little but there's still more snores than I would like to see if it were my report. They are probably related to the times when you are on your back. When we are supine it is quite common for our OSA to worsen and for us to need more pressure to hold the airway open. The snores are indicative of the airway trying to collapse but not progressing further with the EPAP at 12. With lower EPAP the snores progressed to the OAs and all the other stuff you saw that related to obstruction (hyponeas, RERAs, OAs). The CAs/centrals were most likely arousal related...meaning the obstructive stuff caused you to wake up and maybe hold your breath or something which got flagged as a central. They weren't real centrals but instead SWJ centrals. The absence of FLs on your events graph means nothing....you might have been having a ton of Flow Limitatons but fixed pressure Respironics machine don't even flag FLs. Stupid design IMHO....but they didn't ask me.
You probably need a higher pressure when you are on your back than you need when on your side. Same thing can happen for REM stage sleep. I have the REM thing myself...need 6 to 8 cm more pressure during REM where my OSA is about 5 times worse. Supine sleeping doesn't seem to be that much of a trigger for me.
This is why having a machine that can auto adjust can come in so handy....use lower pressures when lower gets the job done and higher only when needed.
At any rate...just continue with these settings for a few nights and lets see what happens.
The peeing during the night....like Jas says...probably related to the OSA events more than salt intake. Did you know that nocturia is one of the most common symptoms of sleep apnea? I had it myself and it was the first symptom to go away once I got my therapy settings optimized (my titration study didn't get it right either).
There's a medical reason behind the nocturia that is caused by sleep apnea....the short version is that when we have an apnea event the heart is stressed and when it gets stressed it dumps a stress hormone called ANP into the blood stream.
https://en.wikipedia.org/wiki/Atrial_na ... ic_peptide
When that stress hormone makes its way to the kidneys the kidneys kick into over drive...and when kidneys work hard we get an abundance of urine produced.
I doubt seriously that your nocturia is related to your diet at all but was instead related to the sleep apnea that wasn't being effectively prevented at the pressures you were using.
Let's get a few nights under your belt and see for sure we are close here...then decide on further options.
I may have to RISE but I refuse to SHINE.
, RE down to 26 (average 48.2), no PP at all (average 12.4). 
One night doesn't not make a trend and I want to see if this holds or not.
