Animals having miserable sleep upside down (6)
I believe the answer is:
pandas
'animals' is the definition.
The answer is an example.
'miserable sleep upside down' is the wordplay.
'miserable' becomes 'sad' (similar in meaning).
'sleep' becomes 'nap' (a nap is a short sleep).
'upside down' says the letters should be written backwards.
'sad'+'nap'='sadnap'
'sadnap' written backwards gives 'PANDAS'.
'having' is the link.
(Other definitions for pandas that I've seen before include "They eat bamboo leaves" , "Black and white bear-like animals" , "Black-and-white Chinese bears" , "patrol cars" , "Black and white bears from China" .)