We describe a case of Wernicke's encephalopathy secondary to thiamine (B1) deficiency in a patient status post-bariatric sleeve gastrectomy. The presenting symptoms of new-onset weakness, diplopia, and confusion in a young female patient raised suspicion for multiple sclerosis (MS), but given a history of bariatric surgery, thiamine levels were checked, revealing significant Vitamin B1 (thiamine) deficiency. This case highlights the importance of thorough history taking, as a misdiagnosis of MS in this case could have resulted in irreversible neurological deterioration and hematological and infectious consequences associated with the inappropriate administration of disease-modifying therapies. It is also important to note that severe vitamin deficiency occurred despite medication compliance.