It's my impression, "Lost Your Marbles" meaning gone a bit crazed, lost your wits, gone Looney Tunes, was an American saying first, and only borrowed in Britain recently, if at all.
What would be a more Brit way of saying it, back during WWII? Is "gone round the twist" sufficiently old?
Or some other colloquialism, more authentic?
"Barmy" should do it. 
'Gone doolally'? - this is from about the right period and was (apparently) used by British servicemen in WWII
'Off your rocker'?
Gone bananas?
I can remember my mother, a starry-eyed young lass at the time of WW11, using both the above quite often.
Oh yes, I'd quite forgotten "gone doolally". That's a great suggestion, Merry.
Likewise "Barmy".
Thanks to you both.
