How often does hypnosis cause distress or worsening symptoms?

The short version: nobody has measured how often hypnosis causes distress, because the trials that use it were built to test benefit, not harm.

Not one record here puts a rate on distress or symptom worsening from hypnosis. The closest thing to a harm count is 6 of 52 people dropping out over limb-liner discomfort, and that was the liner, not the hypnosis [2]. Everything else measures upside: pain scores, fatigue, sleep, propofol use [1][4][5]. The pediatric respiratory review is the only record that even mentions symptom worsening, and it reports none in a case series of 49 patients [3]. A case series where a clinician reports his own success is the weakest possible form of safety data, and it is the best this retrieval offers.

Worth separating the two things you asked about. Symptom worsening is a claim about the treated condition, and the records track that poorly; a meta-analysis of 15 randomized studies in 742 cancer patients reports benefit on nausea, pain, and anxiety, but summarizes effects, not adverse events [5]. Distress is a different animal: abreaction, unexpected emotional flooding, or a false memory formed under trance. None of these records instrument for it, and most included trials admit they did not report adverse effects at all [2]. A trial that never asks about harm will not find it.

Hypnosis is low-risk on mechanism: no drug, no needle, no immune challenge. The real exposure is psychological, and the people most vulnerable are the ones with trauma histories or dissociative conditions, who are also the least likely to be in these trials.

My call: distress from hypnosis is probably uncommon, but there is no honest number, and anyone who gives you one is guessing. Confidence: low.