The most common and most likely answer to this crossword clue is the 12 letter word SOMNAMBULIST
I've seen this crossword clue in Financial Times
S
O
M
N
A
M
B
U
L
I
S
T
Buddy explains!
The straight part
We know that "I am lost and numb" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case i am lost and numb = somnambulist.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.