The most common and most likely answer to this crossword clue is the 8 letter word RECLINED
I've seen this crossword clue in The Daily Telegraph
R
E
C
L
I
N
E
D
More clues leading to the result RECLINED
Buddy explains!

The straight part
We know that "Lying back" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case lying back = reclined.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 RECLINED mean?
RECLINED verb- To cause to lean back; to bend back.
- To put in a resting position.
- To lean back.
- To put oneself in a resting position.
- In a reclining posture.
- Reclinate.