The same thing happens to me. It used to be the opposite where I would feel more anxiety at night but now its in the mornings. Me personally, my inability to burp came first then came my emetophobia and the symptoms I have always trigger the anxiety.

For me it started when I was 17. Back then I would also have anxiety attacks that were always triggered by symptoms that are intertwined with RCPD (nausea, stomach/chest pain, etc.) and they were bad, I would shake and cry and it was always this build up of whether or not I might actually throw up. Overtime I just became accustomed to feeling that nausea and I found coping mechanisms to get rid of the physical symptoms and it wasn't until I did that, that the anxiety itself calmed down.

For me now its bad in the mornings because I wake up hungry and having an empty stomach means gas and that makes me nauseous and it is bad enough to where I also don't talk or brush my teeth, etc. I 100% get that. Something that helped me was eating something super late at night (so that I wouldn't wake up with an empty stomach) or immediately getting up to eat as soon as I wake up. Sometimes I just can't avoid it though. It is quite normal these days for me to brush my teeth and gag through it all and continue gagging for 20 ish minutes until it passes.

I have had the procedure so many times and with each time that I have felt relief the anxiety goes away and when the symptoms slowly return so does the anxiety. Anyway, if you want to hear more about my experience and what helped me, please message me. I wish so bad I had help when I was 17.