If histadelia is high histamine diphenhydramine, is an anti-histamine temporarily regulating my natural histamine levels?

No scientific basis: You can find histadelia on any Google search, but NOT on any serious medical search. There are patients who suffer from high histamine levels, but those are patients who have severe allergic reactions or rare tumors. Diphenhydramine will help such patients, also allergic patients in general, as many are mediated by histamine. However, histaelia is NOT a real disease.