How do you decide when to obtain a brain CT and/or MRI in hospitalized patients with altered mental status?

Always, unless the patient can be quickly awakened by glucose, etc., or it NDR, so I guess this means often.

Patient has altered mental status (AMS). That doesn't mean the patient is always unconscious.

If the patient is unconscious, you will always image them as soon as possible, along with checking for infections, metabolic and electrolyte abnormalities, substance use, and more, as history indicates.