Post-Acute COVID-19 Syndrome (PACS) or Long COVID: This diagnosis is likely due to the patient's symptoms persisting years after COVID-19 infection. The responsiveness to Rizatriptan, a medication often used for migraines, might suggest that the patient's symptoms could be related to migraine-like episodes, which are sometimes seen in PACS. The confusion and sleepiness could be part of a broader spectrum of neurological symptoms associated with Long COVID.

Migraine Variants: Given the patient's response to Rizatriptan, it's possible that the patient is experiencing a form of migraine that includes confusion and sleepiness as prominent symptoms. Migraines can have a wide range of presentations beyond headache.
Sleep Disorders: Conditions like narcolepsy or idiopathic hypersomnia could explain the sleepiness, and while less likely to cause confusion directly, could contribute to it indirectly through sleep deprivation or as part of a broader neurological condition.
Chronic Fatigue Syndrome/Myalgic Encephalomyelitis (CFS/ME): This condition, characterized by profound fatigue, cognitive dysfunction, and sleep abnormalities, could be considered, especially given the post-infectious context.

Subarachnoid Hemorrhage or Other Intracranial Bleeds: Although less likely given the chronic nature of the symptoms, any condition that could cause sudden confusion and sleepiness, such as a subarachnoid hemorrhage, must be ruled out due to its high mortality and morbidity.
Infectious Encephalitis: Chronic or persistent encephalitis from various pathogens (including but not limited to COVID-19) could present with confusion and altered mental status. This diagnosis is critical to consider due to its potential for severe outcomes if left untreated.
Neurodegenerative Diseases: Early stages of neurodegenerative diseases like Alzheimer's disease or frontotemporal dementia could present with confusion and changes in sleep patterns. While less likely in the context of post-COVID symptoms, these conditions have significant implications for patient management and prognosis.

Hashimoto's Encephalopathy: A rare condition associated with Hashimoto's thyroiditis, characterized by cognitive dysfunction, confusion, and altered mental status. It's an important consideration due to its responsiveness to corticosteroid treatment.
Cerebral Vasculitis: Inflammation of the blood vessels in the brain could lead to a variety of neurological symptoms, including confusion and sleep disturbances. This condition is rare but potentially treatable with immunosuppressive therapy.
Prion Diseases: Extremely rare and typically presenting with rapidly progressive dementia, prion diseases like Creutzfeldt-Jakob disease could be considered in cases of unexplained, progressive neurological deterioration.