No he loses his memories when someone successfully attacks him (i.e. he fails his save)
BUT that is fairly hard to do. He is Impervious for attacks PL 10 and below and has a +15 save.
If it were the otherway I would have said when successfully attackING and well that would've sucked.

Though yes, occasionally a very strong personality can supress his personality and he may think he is that person.
I myself enjoy characters with some flaws. Though I try to make it flavorful and not all-encompassing. The whole memory muck up thing probably will only occur every few adventures or so.