Some in catalepsy nodding in assembly (5)
I believe the answer is:
synod
'assembly' is the definition.
(I've seen this before)
'some in catalepsy nodding in' is the wordplay.
'some in' indicates the answer is hidden within the clue.
'SYNOD' can be found hidden inside 'catalepsy nodding in'.
(Other definitions for synod that I've seen before include "Assembly of the clergy" , "Ecclesiastical assembly" , "Council of clergy to discuss policy" , "Forum for discussing" , "Church council" .)