Older antihistamines were anticholinergics, the latter of which are famous for causing vivid auditory, visual and somatic hallucinations.

Well, not just drugs-children are more likely to experience hallucinations even without drugs.

I still have vivid memories of experiencing what (in hindsight) I realise were hypnopompic hallucinations, around the age of 6 or 7. I wasn’t taking any regular medications, that I can remember. But, I grew out of it, as kids usually do.

A fun aside here: experiments in which people who’ve taken hallucinogens are placed in brain scanners reveal activation patterns which look an awful lot like what we see when we put small children in brain scanners, and this somewhat accords with the neurogenesis vs pathway pruning see-saw model of brain development.

I’ll say personally my experiences with psychedelics brought back memories of childhood - how I engaged with the world, how my mind would go off down different paths, the intensity of focus - so, you’re probably not far off here.

I always said psychedelics reduce you to a child, with reduce having no negative connotation, just a word that describes the experience. It's like sending your perception back in time in some ways, while retaining some matured aspects.

Also known as "delirium". They cause delirium. Benadryl (DPH) for example does that. It is very dysphoric.

Lower doses can induce hallucinations before it becomes full on delirium that you see in higher doses. You'll regularly hear about people seeing "spiders" after taking 25-50mg of Benedryl, the recommended dose.

I think that may be more common in the elderly. I had full-on delirium from 5 x 50 mg, however. I would not recommend. It took me months for my body to recover. The auditory hallucinations lasted the longest (2-3 days), but my body and my mind was a wreck for months. Thanks to our beautiful hospital that did not administer the antidote for anticholinergic toxicity.