Well, I wonder too, Daddima. If you went to a shop to buy champagne the assistant is surely going to smile and enquire, "Something to celebrate?" You'd have to return the smile and give a polite yet non-committal answer. I think. perhaps a white lie is in order.
There's an excellent book by Hunter Davis about the early years of the lottery and its winners which explores that very subject which is worth a read. It needs a 2nd volume - what about it HD if you're on here?
What would I do? Gosh, I'm not sure. I think I'd do the normal thing at such moments - put the kettle on and contemplate the situation.
I wouldn't want to go mad - after all, a Lamborghini on the driveway would be a bit of a giveaway, wouldn't it?