And if I were that person, I'd immediately summon the FA and explain that I'm not baby-sitting an airsick young child. Nothing personal, but I see this, essentially, as a threat, i.e. "Move, or else . . ."

If, when you arrived at the airport, you discovered that your seats had been changed, why wouldn't you raise he!! with airline and get what you need or, worst case, just take another flight? Back when I had a severe flying phobia, I wouldn't fly unless I had a window seat (looking out helped me). I was in a number of situations in which, due to equipment changes, late aircraft arrivals and cancellations, I wound up booked into something other than a window. I just took a later flight (in some cases, much later). It would never have occurred to me to say to a stranger who wouldn't switch seats, "Well, alright, but when I have a panic attack and start screaming, you're going to have calm me down." I would never try to make my problem a problem for someone else.

I'm sure you're a perfectly nice person, but I don't understand your thinking at all.