The most common and most likely answer to this crossword clue is the 12 letter word RESTLESSNESS
I've seen this crossword clue in The Daily Telegraph
R
E
S
T
L
E
S
S
N
E
S
S
Buddy explains!

The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does RESTLESSNESS mean?
RESTLESSNESS noun- The state or condition of being restless; an inability to be still, quiet, at peace or comfortable.