Thursday's (October 17) EU/UK agreement in Brussels rallied sterling a full per cent.
And shares to a year-and-a half peak - as investors reversed out of safe-havens, including bonds: yields surged as bunds, gilts and others sold off.
The moves triggering a wave of optimism on Europe's markets.
Baader Bank's Robert Halver.
(SOUNDBITE) (German) HEAD OF CAPITAL MARKET ANALYSIS AT BAADER BANK, ROBERT HALVER, SAYING:
"The danger of a no deal on October 31, on Halloween, is definitely off. In an emergency there will be a Brexit extension... but overall, Europe is happy again."
But Britain's Brexit deal isn't in the bag yet - Prime Minister Boris Johnson still needs the approval of parliament.
That may - or, if the votes don't stack up - may not come when it meets on Saturday October 19th.
And as that doubt began to sour the new mood, the pound fell back.
As for the volatility: Bill Blain of Shard Capital says 'brace for more'.
SOUNDBITE (English) BILL BLAIN, STRATEGIST, SHARD CAPITAL, SAYING:
"There's not really enough time for parliament to debate it properly and agree what goes through. So the only thing I can say with any certainty on Brexit is that it's going to remain very uncertain."
After hitting a five-month peak just shy of one dollar 30 - sterling slithered back to a loss of 0.2%.
The pan-European STOXX 600 gave up most of its gains.
Though the pound's slide did boost the UK's exporter-heavy FTSE 100.
For Britain's Brexit-hardened share traders, the clouds still have a silver lining.
