Acute Stroke: This is the most likely diagnosis due to the combination of sudden onset confusion, slurred speech (dysarthria), and disequilibrium, which are classic symptoms of a stroke, particularly one affecting the brainstem or cerebellum.

Alcohol Intoxication: Confusion, slurred speech, and disequilibrium can be symptoms of alcohol intoxication. The clinical presentation can mimic that of a stroke, making it essential to consider and rule out through history and toxicology screens.
Medication Side Effects: Certain medications, especially sedatives, anticholinergics, and some antidepressants, can cause confusion, slurred speech, and balance issues as side effects.
Infections (e.g., Urinary Tract Infection, Pneumonia): In elderly patients, infections can present with confusion (delirium) and may also cause slurred speech and disequilibrium due to systemic effects or direct involvement of the central nervous system.
Metabolic Disorders (e.g., Hypoglycemia, Hyperglycemia): Both low and high blood sugar levels can lead to confusion, slurred speech, and disequilibrium, making prompt blood glucose testing crucial.

Status Epilepticus (especially Non-convulsive Status Epilepticus): This condition can present with confusion and altered mental status, and while seizures are a hallmark, non-convulsive forms may not have overt seizure activity, making EEG crucial for diagnosis.
Meningitis or Encephalitis: Infections of the meninges or brain can cause sudden onset of confusion, speech changes, and balance problems, along with fever, headache, and stiff neck.
Subarachnoid Hemorrhage: A sudden, severe headache (often described as "the worst headache" of their life) accompanied by confusion and possibly slurred speech and disequilibrium, requires immediate imaging to diagnose.
Wernicke's Encephalopathy: This condition, caused by thiamine deficiency, can present with confusion, ataxia (disequilibrium), and ophthalmoplegia, and is a medical emergency requiring immediate thiamine supplementation.

Multiple Sclerosis (MS) Exacerbation: While MS is more commonly associated with optic neuritis, spinal cord symptoms, and brainstem symptoms, an exacerbation could potentially present with confusion, slurred speech, and disequilibrium, especially if there are lesions in strategic areas of the brain.
Creutzfeldt-Jakob Disease: A rare, degenerative, fatal brain disorder that can cause a range of neurological symptoms, including confusion, speech difficulties, and ataxia, though it typically progresses rapidly.
Hashimoto's Encephalopathy: A rare condition associated with Hashimoto's thyroiditis, characterized by encephalopathy, which can include confusion, altered mental status, and sometimes seizures, with or without thyroid dysfunction symptoms.