delirium vs on the brain

delirium

noun
  • Wild, frenzied excitement or ecstasy. 

  • A temporary mental state with a sudden onset, usually reversible, including symptoms of confusion, inability to concentrate, disorientation, anxiety, and sometimes hallucinations. Causes can include dehydration, drug intoxication, and severe infection. 

on the brain

prep
  • Obsessively in mind. 

How often have the words delirium and on the brain occurred in a corpus of books? (source: Google Ngram Viewer )