[Jugurtha]

We call it "Madeleine de Proust" in French.

https://fr.wikipedia.org/wiki/Madeleine_de_Proust

https://en.wikipedia.org/wiki/Involuntary_memory

"Proust Effect" or something like that in English.

[jwmcq]

I think I've seen "Madeleine Moment" most often in English.