Hi seishin. I have been experincing the throat closing sensation you describe, lying down, sitting up, whatever position it seems. As I was waking up gasping for breath lying flat, I have now been sleeping at a 30 degree angle for about five weeks, which seems to lessen, but not completely get rid of the problem. I would say it took me a while to adjust to this new position and I bought a new V neck pillow, which I use with another five pillows to support my back correctly.
As I don't have a diagnosis I can't advise you on what to do MG-wise but all I can find is to try and relax as much as possible when it is happening, usually mine passes the really bad stage within 10-15 minutes.