Guillain-Barré Syndrome (GBS): This is the most likely diagnosis due to its classic presentation of acute onset, symmetrical, and ascending weakness, often including bifacial weakness. GBS is an autoimmune disorder that typically follows a minor infection.

Myasthenia Gravis: Although more commonly associated with ocular and proximal muscle weakness, myasthenia gravis can present with bifacial weakness, especially in the context of a myasthenic crisis. The weakness is typically fluctuating and worsens with use.
Lyme Disease (Neuroborreliosis): In endemic areas, Lyme disease can cause a range of neurological symptoms, including facial nerve palsy, which can be bilateral, presenting as bifacial weakness.
Tick Paralysis: Caused by the neurotoxin from certain tick bites, this condition can lead to ascending paralysis, including facial weakness, which can be bilateral.

Botulism: A potentially life-threatening condition caused by the toxin from Clostridium botulinum. It presents with descending paralysis, starting with cranial nerves, which can include bilateral facial weakness. Prompt recognition is crucial for treatment.
Diphtheria: Although rare in areas with good vaccination coverage, diphtheria can cause neurological manifestations, including cranial nerve palsies, due to the toxin produced by Corynebacterium diphtheriae.

Fisher Syndrome: A variant of Guillain-Barré Syndrome, characterized by the triad of ophthalmoplegia, ataxia, and areflexia. Bifacial weakness can be a part of the presentation.
Mitochondrial Myopathies: Certain mitochondrial disorders can present with progressive external ophthalmoplegia and other muscle weaknesses, which might include facial muscles, though acute onset would be unusual.
Congenital Myasthenic Syndromes: These are a group of rare genetic disorders affecting the neuromuscular junction, which can present with fluctuating muscle weakness, including facial weakness, though typically from birth or early childhood.