Extreme enthusiasm (5)
(Other definitions for craze that I've seen before include "Fashion, fad; crack" , "Short-lived fashion" , "Fad, short-lived enthusiasm" , "latest thing" , "Widespread fad" .)
'extreme enthusiasm' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for mania that I've seen before include "Aberration" , "thing" , "fixation" , "Obsessional enthusiasm" , "A (violent) mood disorder" .)