The most common and most likely answer to this crossword clue is the 5 plus 3 letter word CHILL OUT
I've seen this crossword clue in The Guardian
C
H
I
L
L
O
U
T
More clues leading to the result CHILL OUT
- Prelude to a fever abroad? Don’t worry
- Relax belt while undressed inside
- Revealed after letter gets students to calm down
- Laid up in house with minor wound for dressing, relax
- Kid almost a yob? Relax
- Kid almost gets yob to relax
- Relax with honourable Ivy League leaders in power
- Kid endlessly pursued by yob? Calm down!
- Young person tailed by thug needs to relax
- Cut oil blend to hair lotion initially to relax
Buddy explains!

The straight part
We know that "Don’t worry" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case don’t worry = chill out.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 CHILL OUT mean?
CHILL OUT noun- A period of quiet, rest and relaxation, especially after a party etc.
- A genre of house music and ambient music with an ethereal sound and a driving beat.