In the literature, several cases of an association between hyponatremia and psychotic symptoms have been reported. We present the case of a young Caucasian male presenting with rapid, incoherent speech, religious and megalomanic delusions, and emotional lability. The patient was described by his relatives as being healthy until a few days before admission. He had no significant medical or psychiatric history, except a short drug-induced psychotic episode a few years earlier. Somatic workup showed moderate hyponatremia, but no other abnormalities. Tests for narcotics, in particular, were also negative. Antipsychotic treatment with risperidone was initiated. After normalization of sodium levels using intravenous saline, the patient remitted within a few days and risperidone was discontinued on day 3. He was discharged by day 13 without further pharmacological treatment.Dysfunction of voltage-gated ion channels, particularly sodium and calcium channels, has been implicated in the pathogenesis of bipolar disorder. We therefore assume a causal relationship between hyponatremia and manic-psychotic symptoms in our patient. Hyponatremia was most likely induced by excessive water intake during a period of fasting in the context of a wellness practice.