Andy, I suspect that your computer's HD file became corrupt, such that it thought you were in North America. Accordingly, it was spinning backwards. Once you logged out & back in, the HD reversed its spin and all was put to right.  In Australia, hard drives must be installed upside down.
Jon
macOS 11.7.10, iMac Retina 5K 27-inch, late 2014, 3.5 GHz Intel Core i5, 1 TB fusion drive, 16 GB RAM, Epson SureColor P600, Photoshop CC, Lightroom CC, MS Office 365
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