And I discovered why this is a bad idea.
Slightly trippy games with suddenly shifting perspective are fine at home, not so much when walking down the street talking on the mobile. Suddenly I was flat on my face with the wind knocked out of me and a sense of having had a moment of serious confusion.
Luckily, nothing broken and no serious cuts or scrapes. Just the sort of grazes on knees and elbows you get when very small, and a general sense of having been hit very hard with a mallet.
Going to bed with migraine was no fun, nor was having a bath, or trying to write.
I am very grumpy and have discovered a dumb thing I SHALL NEVER DO AGAIN.