to use or abuse a
hallucinogenic drug of the deliriant variety.
The term is used most predominantly by those who frequent 420chan's deliriant board when referring to ingesting massive amounts of diphenhydramine (Benadryl in the US).
Delving is notoriously unpleasant and often terrifying to the user. Yet some drug users are drawn to delving by the very
realistic looking
hallucinations of non-existant people and objects, that are not seen on other types of drugs.