What conditions could cause delusions, seizures, and headaches?

Many: Nearly any medical condition can cause delirium or confusion resulting in delusions, in a susceptible person. This includes fluid & electrolyte imbalance, infections, drug & alcohol withdrawal, toxicity from drugs & alcohol, metabolic disorders, postoperative states (esp in elderly), stroke, and neoplasms that metastasize to brain. Also, degenerative neurological conditions can cause these sx.