All the evidence I have so far, from this bout of trouble and the one eighteen years ago, points to the motion sickness striking me when I am laying down and/or asleep. As I observed previously in this thread, once I am up and vertical without symptoms I will be fine for the rest of the day. Researching the Eppley manoeuvre tells me it is a series of positions of the head which are taken and held for a while to allow the inner ear fluid and whatever is wrong with it to "drain" to a position where it does not cause issues with motion and balance.
Perhaps tossing and turning in the night can cause the opposite effect and put the dodgy fluid where it can wreak havoc as I get up?
I am fairly sure that the effects of a little bit of air turbulence do not spark me off as I "committed aviation" for a couple of hours today and I was absolutely fine.
Rans6..................