Not to mention being undisturbed (3,5)
I believe the answer is:
I believe this is a double definition.
'not to mention' is the first definition.
(both can be used to refer to another point)
'undisturbed' is the second definition.
'being' is the link.
(Other definitions for let alone that I've seen before include "Not to mention - much less - avoid" , "Not to mention (thing)" , "Not to mention, never mind" , "Don't bother someone - allow to be solitary" , "Don't touch" .)