An approach to the confused patient...think about 4 major categories.
1. Drugs/Toxins: make sure you ask about both prescribed and non-prescribed drugs - like herbal supplements, traditional medications, and street drugs. Also, remember to ask about both intoxication and withdrawal effects (eg. Alcohol, Benzodiazepines).
2. Infection: think about common sites - like urinary tract, pneumonia, intra-abdominal, and endovascular sources of infection. Also consider less common areas like meningitis and cerebritis.
3. Metabolic: "pick an organ and make it fail". Common things include hyper/hyponatremia, hyper/hypoglycemia, hypercalcemia, hepatic or uremic encephalopathy, hyper/hypothyroidism, hypercarbia or hypoxia, etc.
4. Structural: think big, like heart (eg. myocardial infarction), gut (eg. ischemia, obstruction), brain (eg. mass, infarct), muscle (eg. rhabdo), lung (eg. pulmonary embolus), etc.