Doctor I ran to with diagnosis for disorder (15)

'disorder' is the definition.
(I know that disorganisation is a type of disorder)

'doctor i ran to with diagnosis' is the wordplay.
'doctor' is an anagram indicator.
'with' means one lot of letters go next to another.
'i'+'ran'+'to'='iranto'
'iranto' after 'diagnosis' is 'diagnosisiranto'.
'diagnosisiranto' is an anagram of 'DISORGANISATION'.

'for' acts as a link.