bad trip
bad trip {n.}, {slang}, {also used colloquially}
A disturbing or frightening experience, such as terrifying hallucinations, while under the influence of drugs; hence, by colloquial extension any bad experience in general.
Why's John's face so distorted? — He had a bad trip.
How was your math exam? — Don't mention it; it was a bad trip.
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Source: A Dictionary of American Idioms