What is the meaning of the idiom 'foot went to sleep'?
It's a figure of speech rather than an idiom. When standing for a long length of time, your own weight can put pressure on the nerves of your legs. It can also put pressure on the blood vessels and restrict normal flow of blood to the nerves. Either way it makes the nerves act erratically.This is characterised in a loss of feeling or movement in the affected limb, and hence, the limb has 'gone to sleep'.