Why is sixes and sevens a phrase used to describe "crazy"?

In the UK, I have heard this phrase and wonder what it's origin is.... anyone from the UK know the meaning?

It doesn't mean crazy; it means confused, don't know what to think or do.

Example: "Now that I can't book the village hall for my party, I'm all at sixes and sevens."

Probably originates from some old card game or dice game

I've never heard it lol maybe it's from London lol

It doesn't so much mean 'crazy' as 'all mixed up' or 'in a muddle'.
I've no idea where the saying comes from, though.

Six and seven is probably a corruption of cinque and sice, which is the French for the numerals five and six. Some may feel that this is a step too far, and the theory does set the folk-etymology antennae twitching

There are two other stories that contend for the honour of being the source of this phrase (or one of the versions of it at least). One is the biblical text - Job 5:19 (King James Version):

"He shall deliver thee in six troubles: yea, in seven there shall no evil touch thee."

There several candidate origins, more than one of which may hold true.
I still think the best answer to it's popularity comes from the order of precedence of the London livery companies,.two being in dispute over which was founded first.

These companies, six and seven on the list, finally agreed to swap places every year, and so their order in the annual Lord Mayor's parade alternates.

There are earlier similar phrases, and six and seven were risky bets in a French dice game of Hazard, but the usage "to be confused", or "to keep changing your mind" owes more to the London livery companies, I suggest.

It would also explain a London-centred popularity to the term.

(I'm a freeman of a livery company, and, having taken up through this my Freedom of the City of London, as have many others, this does give, at least notionally, certain rights:

"Apocryphally, a freeman has the right to drive sheep and cattle over London Bridge, or to carry a naked sword in public; or if officers of the City of London Police find a freeman drunk and incapable, they will bundle him into a taxi and send him home rather than throw him in a cell and later charge him. The benefit of immunity from prosecution for being drunk and disorderly has long since disappeared, if indeed it ever existed. However the droving rights were exercised on June 17, 2006 when a flock of about 30 sheep was driven across the Millennium Bridge to mark the start of London Architecture Week.")