the term 'delusion' unpacks
, as the post-modernists used to say.
many cultures - and some anthropologists say all cultures - have a tradition or two or three of belief in fairies and other extradimensionals which they believe are viewed by highly specialised adepts using sensoria not activated in most individuals. in some cultures these are perhaps unrealistically revered as sooth-sayers, and sure there's a danger of corruption and unethical abuse of trust.
but since the conquest with its commands to 'kill all witches', and 'let not a wizard to live', which are still being given from pulpits worldwide to infants and adults alike at various depths of hypnosis, you have people who don't see fairies, only angels and devils, and believe fairies to be of the devil; and later, in 19th/ 20th century, they see only germs and criminals as real, they've been set up in judgment over the seers, and sometimes they still set themselves
up to decide in their minds whether i'm 'sane' or 'psychotic', or a liar, i.e., culpable or curable, if i say i saw a fairy and it spoke audible words to me and i felt it when it kicked me and pinched me and bit me till i'd admit that i saw it.
this judgment goes inevitably way beyond the evidence, which they have not viewed, in declaring it hallucinatory and the 'seer' delusional. in other words, it is unscientific to claim to know the cause of an event you have never experienced.
if you have insufficient data you should be aware of that and suspend judgment.
regarding the question of 'delusionality', the language of psychiatry is horrendously loaded,
- and imo reprehensibly so this far into the postmodern period - as the anti-psychiatrists of the 60s famously protested, although they didn't explore that.
'delusional', which means only 'mistaken', becomes in psychiatric terms 'a symptom of psychosis', which means in Anc Greek: 'pertaining to, or characterised by the features of, or possessing, a soul', for which there is a horrendously terrifying 'cure' which damages the receptors so that they can no longer function, reducing the victims to shuffling zombies who are considered to be cured because they no longer 'hallucinate' or care enough to protest against the treatment. the following quote is old, but the drugs are still in use despite protests of patients and psychiatrists. the treatment and the approach to treatment persist. recent work can them to look and act more normal, but the drugs still work by disabling natural functions in the brain that are judged without evidence to be 'bad'. http://www.sntp.net/drugs/thorazine.htm
this is not a horror fiction. it is hard reality.
a chinese proverb
he who knows and knows he knows
he is a wise man seek him
he who knows and knows not he knows
he is asleep, wake him
he who knows now and knows he knows not
he is a child, teach him
he who knows not and knows not he knows not
he is a fool, shun him.
though maybe that's a rather peremptory reaction to a fellow human in a loop.