What are the causes of SIADH ?

A 64-year-old male presents to the emergency with progressive altered behavior for 10 days, and seizures 1 day back. He is a known diabetic for 20 years and hypertensive. BP 140/90, RBS 130 mg, creatinine 1.2 mEq/L, Na 110 mEq/L, K 5.0. There is no history of seizures and CT head is normal. How would you evaluate this patient?

What are the causes of SIADH ?