It’s silly to get back with a dizzy head (4)
'it's silly' is the definition.
(I've seen this before)
'back with a dizzy head' is the wordplay.
'back' becomes 'aft' (associated in meaning).
'with' means one lot of letters go next to another.
'head' indicates taking the first letters.
The initial letter of 'dizzy' is 'd'.
'aft' put after 'd' is 'DAFT'.
'to get' acts as a link.
(Other definitions for daft that I've seen before include "'Silly, foolish (4)'", "Informally silly or foolish", "Idiotic", "Stupid", "'---- as a brush': dotty".)