When I look down... objects appear nearer in sunglasses? Why?

Because MOST sunglasses don't have to pass optical quality standards and A LOT of those lenses are slightly distorted. Especially sunglasses with a lot of "wrap"... if they wrap around your head a bit and are curved around your face, this could be the issue.

P.S. Shail--I apologize it's taken me so long to get to your question.