These sound like potentially pretty serious problems:

> felt weak all the time, lacking all the energy to run and play sports like his friends

> Besides relentless fatigue, other common symptoms appear to include severe headaches and stomach cramps.

> plagued with an irritable bowel

> “I would go more than a week without a bowel movement while ‘hungry’, and feel nausea if I ate anything other than my ‘cure food’,”

I don't know what's going on, but dismissing it as delusion seems unhelpful, unkind, and untrue.

People who suffer from 'electromagnetic sensitivity' also feel symptoms when they're around known wifi hotspots.

Doesn't make it any more true.

Just because some symptoms could be psychosomatic doesn't make them any less debilitating. Writing off peoples symptoms because you think they're psychosomatic seems a little cruel.

With EMS, the symptoms are real whether or not those people can actually detect wifi hotspots. Similarly, it seems like the vampires genuinely have symptoms which are cleared up by drinking blood.

Now, if someone believes "wifi hotspots give me headaches", that's untrue. They only get headaches when they believe there's a hotspot nearby. This has been demonstrated in general, and it should be easy to demonstrate to any individual sufferer. After that demonstration, if someone continues to believe that wifi hotspots give them headaches, then it may be reasonable to call them delusional. But that doesn't make their symptoms go away.

What specific belief do you think vampires have, that you think has been demonstrated untrue?