It seems to be quite common. The Newcastle Chronicle reported on a case in the summer, where a 59 year old Geordie woman who suffered a stroke woke up in hospital speaking in an accent which her friends described as sounding like a cross between Jamaican and Eastern European!

She told the Chronicle, "Everybody asks where I'm from and if I say Westerhope they just laugh,"

http://icnewcastle.icnetwork.co.uk/eveningchronicle/eveningchronicle/tm_objectid=17325978%26method=full%26siteid=50081%26headline=geordie%2dto%2dan%2deast%2deuropean-name_page.html

As terrifying for the French as much as anyone else, at least according to Mark Steyn (a man who only took up journalism because Goldman Sachs couldn't afford him). An excellent article from a superb journalist.

The Foolishness of France by Mark Steyn (originally published in Maclean's)

Extracts

'If you had vaguely assumed that the now routine comparisons of Israelis to Nazis derived from an antipathy to Ariel Sharon or the post-1967 transformation of the Zionist Entity from plucky embattled underdog to all-conquering military behemoth, it’s sobering to be reminded that the French were doing the Israelis-are-the-new-Nazis shtick within ten minutes of the end of the Second World War. Jews, wrote the consul-general Rene Neuville, in a lengthy cable from Jerusalem in 1947, are “racist through and through… quite as much as their German persecutors”. The dispatches of Pierre Landy, French consul in Haifa, rely heavily on “the Israeli Gestapo” and similar formulations. In public the political class was usually more circumspect, though not always. President de Gaulle famously raged at a press conference that the Jews were “an elite people, self-assured and domineering” with “a burning ambition for conquest”. In the ensuing controversy, M le President assured the Chief Rabbi that he’d meant it as a compliment.'

'But, with the largest Muslim population in western Europe increasingly hostile to the French state and all its works, the Fifth Republic, concludes David Pryce-Jones, “is acquiring an internal reality as ‘une puissance musulmane’ on lines quite different from anything envisaged by those who have fostered this intellectual illusion”. Painstakingly culled from decades of extraordinarily smug dispatches in the Quai’s archives, this book (at a time when the striped-pants set are back in the ascendancy in Washington) is a sobering lesson in the limitations of foreign policy “expertise”. Pryce-Jones’ title is especially well chosen: in the end, French policy has been a betrayal of France itself.'

Yes, UKDP got in before me on that one and there's the one who developed an American accent some time back. I'd love to wake up speaking Rab C. Nesbitt.

I would love it if someone like Brian Sewell woke up speaking cockney one morning.