Introduction: We report a case of sudden loss of consciousness due to hypoglycemia in the terminal stage of cancer. Case: A 73-year-old man underwent craniotomy in 2016 and was diagnosed with solitary fibrous tumor. In 2022, his brain tumor recurred and he was admitted to our hospice. On the morning of the 120th day after transfer, the patient suddenly developed impaired consciousness. Blood tests showed hypoglycemia (33 mg/dL), and intravenous glucose injection improved his loss of consciousness, leading to a diagnosis of impaired consciousness due to hypoglycemia. After various examinations, hypoglycemia due to extrapancreatic tumor (non-islet cell tumor hypoglycemia: NICTH) was strongly suspected. Discussion: NICTH is considered to be caused by excessive secretion of an insulin-like substance (high molecular weight insulin-like growth factor (IGF-)II) from the tumor. In patients who are exposed to hypoglycemia for a long period of time, central nervous system symptoms such as impaired consciousness may suddenly develop without sympathetic symptoms. NICTH should be considered as a differential diagnosis in patients with delirium, impaired consciousness, or convulsive seizures and a large tumor, although it is not easy to prove the excessive secretion of high-molecular-weight IGF-II, especially in the terminal stage of cancer.