Falling back when nursing again (10)

'falling back' is the definition.
The definition and answer can be both to do with motion as well as being present participle verbs.
Maybe you can see a link between them that I don't see?

'nursing again' is the wordplay.
I cannot quite understand how this works, but
'again' could be 're' (prefix meaning 'again') and 're' is found in the answer.
The remaining letters 'treating' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).

'when' acts as a link.

Can you help me to learn more?