All At Sea

Meaning:

In a state of confusion and disorder.

This is an extension of the nautical phrase 'at sea'. It dates from the days of sail when accurate navigational aids weren't available. Any ship that was out of sight of land was in an uncertain position and in danger of becoming lost. 'At sea' has been in use since the 18th century, as here, in Sir William Blackstone's Commentaries on the laws of England, 1768:

"If a court of equity were still at sea, and floated upon the occasional opinion which the judge who happened to preside might entertain of conscience in every particular case."

The earliest reference to 'all at sea' in print that I can find is from The Times, August 1814:

"The Peacock, Wasp, Adams and Syren sloops of war and Hornet schooner, were all at sea when the last accounts reached Halifax."