The most common and most likely answer to this crossword clue is the 8 letter word FRAZZLED
I've seen this crossword clue in The Guardian
F
R
A
Z
Z
L
E
D
Buddy explains!
The straight part
We know that "totally exhausted" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case totally exhausted = frazzled.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 FRAZZLED mean?
FRAZZLED verb- To fray or wear down, especially at the edges.
- To drain emotionally or physically.
- Frayed at the edges
- Stressed and exhausted either physically or emotionally