Welcome to the forum. It isn't clear how you came to the prescribed settings of 4-9, with EPR of 3. How was that determined, and under whose auspices?
Almost universally across subjects, people cannot/do not abide that lowest setting of 4 cm. They feel air starved and it begets anxiety if nothing else. It's not great for settling in towards sleep. Mine is set at 5.6 currently, which works well for me. You might be well advised to up yours to 5 and see how that feels for the next five or six nights minimum.
Waking up groggy, and not feeling well rested as the day progresses, is unfortunately a common complaint across the board. Some don't feel that way after a few days even, but many report here over the years that PAP therapy that seems to be well-dialed-in just doesn't make them feel better.
I don't know what to make of your startle, but if you awaken in stages and your machine senses it, it may reduce your pressure and you'll awaken to that miserly 4 whole cm of pressure. Just sayin'....
Your stats say there's a short-lived 'large leak'. Somewhere that night you deformed or displaced the mask sufficiently that it couldn't seal, and the rest should be obvious. It is almost certainly positional. Your chin fell hard against a pillow, or your curled arm, or something, and the mask was knocked askew. It isn't all bad because some people remove their masks entirely without realizing it...several times each night. Anyway, if your mask does continue to get displaced, you may have to change pillows or use a cervical collar to help your relaxed head to stay better oriented to your body and your pillow.
There are some real prize fighters here who will help you to get more from your therapy. Please wait for them to chime in. I'll keep reading to see what they can offer you.
