How scared you must be, lacking a sense of humour (7)
I believe the answer is:
witless
'how scared' is the definition.
The answer and definition are not the same part of speech. However, adjectives and past participle verbs sometimes mean the same thing.
'must be lacking a sense of humour' is the wordplay.
I cannot quite see how this works, but
'lacking' could be 'less' (I've seen this in another clue) and 'less' is located in the answer.
'sense' could be 'wit' (I have seen 'Good sense' mean 'wit' so perhaps 'sense' could also mean 'wit') and 'wit' is found within the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
'you' acts as a link.
Can you help me to learn more?
(Other definitions for witless that I've seen before include "Out of one's mind (maybe scared)" , "Daft" , "Lacking sense, understanding or judgment" , "Foolish, stupid" .)