The most common and most likely answer to this crossword clue is the 13 letter word HALLUCINATION
I've seen this crossword clue in The Times
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More clues leading to the result HALLUCINATION
Buddy explains!

The straight part
We know that "trip" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case trip = hallucination.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 HALLUCINATION mean?
HALLUCINATION noun- A sensory perception of something that does not exist, often arising from disorder of the nervous system, as in delirium tremens; a delusion.
- The act of hallucinating; a wandering of the mind; an error, mistake or blunder.