Patient describing rotter's dramatic fall (7)
I believe the answer is:
cascade
'dramatic fall' is the definition.
(I've seen this before)
'patient describing rotter's' is the wordplay.
'patient' becomes 'case' (synonyms).
'describing' is an insertion indicator (describe can mean to form the outline of).
'rotter' becomes 'cad' (I've seen this in other clues).
'case' enclosing 'cad' is 'CASCADE'.
(Other definitions for cascade that I've seen before include "Shower" , "Outpouring" , "Small waterfall or series of them" , "Dramatic fall" , "Waterfall or deluge" .)