Welcome to YT.
Since this is something that sometimes shows up because of an underlying condition, have hypothyroidism and myastenia gravis been ruled out?
Is your pup on any drugs for it? Metoclopramide (Reglan)? What food consistency works best for you? Have you tried the sitting up position for eating yet?
My girl may or may not have a mild case. It's doubtful, but she does have some very similar symptoms at times to what would be expected.