Unnecessary hype leads to severe sadness (8)
I believe the answer is:
needless
'unnecessary' is the definition.
(similar in meaning)
'hype leads to severe sadness' is the wordplay.
'hype' becomes 'needle' (I can't justify this - if you can you should believe this answer much more).
'leads to' says to take the initial letters.
The first letters of 'severe sadness' is 'ss'.
'needle'+'ss'='NEEDLESS'
Can you help me to learn more?
(Other definitions for needless that I've seen before include "Without reason" , "Lessened, being without good cause" , "Gratuitous" , "Lessened, as not required" , "uncalled for" .)