Thanks for the kind and useful response, everyone. (Suffice to say that I dare not tell my wife this tale....).
I plan to start my IMC later this year, so it has probably been a timely and salutary lesson about how easy it is to become distracted and disorientated.
However, in the short term I think I'll certainly be a bit more choosey about the conditions that I fly in. Quite apart from the experience out of "the twilight zone", being rattled about like an ice-cube in a cocktail shaker isn't actually much fun.