Something repeated, or fallen into, endlessly? (6)
I believe the answer is:
mantra
'something repeated' is the definition.
(a mantra is a repeated phrase or incantation)
I can't explain the rest of the clue.
(Other definitions for mantra that I've seen before include "Buddhist aid to concentration" , "Sacred text used as incantation" , "Word or phrase repeated as aid to concentration" , "Hindu word or phrase as aid to meditation" , "Repeated incantation" .)