The sleep starts you describe Frog are termed as hypnic jerks and is related to the myoclonus family of symptoms of involuntary muscle twitches. I get these sometimes like you when I am just nodding off to sleep, sometimes during meditation - which paradoxically is NOT relaxing (!) - and I also get them when I am fully with it. Sitting there with a client and either a leg, or occasionally my whole body, has a big ol' twitch. Very embarrassing.
These started during my Cymbalta withdrawal last November, but they have reduced significantly. They come back and are consistent with stress levels, but during "normal" operation, they are very few and far between. We are talking less than 2-3 minor twitches a day.
Tough call on the Christmas trip and ultimately only you can decide. Maybe a double dose of Dramamine will help you through the flight! If you are one of these people that find the anticipation worse than the actual event - as I am - then I would do my best to treat it as an exposure and have the Xanax on standby. Once the trip out goes well, the return trip will be much smoother. My anxiety has got so much better in the last 6 months, but trips away are one of the last things to conquer...