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.
Harv 27" i7 iMac (10.13.6), iPhone Xs Max (12.1)
Those who can make you believe absurdities can make you commit atrocities. ~Voltaire
