He'd already been infested with worms likely all over his body. Hallucinogenic substances are well known to excite helminth parasites of many species. There's even at least one peer reviewed scientific paper that I know of, there may be more similar papers, studying how flukes have been known to "dance" in unison or patterns, collective all of them in a victm(host) when the victim was under the influence of a hallucinogenic drug. I'll try to find a like to it. I can imaging this phenomenon could be extremely disturbing even traumatic to someone not expecting to experience it.