Though well-fed, perhaps, keels over! (5)
I believe the answer is:
sleek
'though well-fed' is the definition.
I can't judge whether this definition defines the answer.
'keels over' is the wordplay.
'over' says the letters should be written backwards.
'keels' reversed gives 'SLEEK'.
'perhaps' is the link.
Can you help me to learn more?
(Other definitions for sleek that I've seen before include "Lustrous" , "With a smooth, gleaming surface" , "Smooth and shiny" , "with glossy coats" , "Well groomed" .)