Orientation

When I was in hospital recently I spent a few days lying on my side. When I finally opened my eyes everything had rotated though 90 degrees. People were walking on the wall. Panicking, I moved my head to an upright position and the scene slid through 90 degrees back to ‘normal’.  This happened more than once. 

It reminded me of a psychology experiment I saw on TV. The experimentee was fitted with some glasses which inverted everything in his field of vision. He found movement very difficult for a few days but then he adjusted to the device and was able to go about the world as normal. His vision did not seem to him to be upside down.  Of coarse the image on our retina is inverted anyway so we all compensate for this all the time. 

When the glasses were removed, he saw the world upside down once more, until his brain made the adjustment and his vision returned to ‘normal’.

It is disturbing to see a map like this even though we know it is an arbitrary convention which puts North at the top. 

Now here’s a question:  a mirror inverts things laterally (from left to right). Why doesn’t it do the same vertically (from top to bottom)?