Guillain-Barré Syndrome: An autoimmune disorder that occurs when the body's immune system mistakenly attacks part of its peripheral nervous system, leading to muscle weakness, and sometimes paralysis. The rapid onset of bilateral limb weakness over a few days is consistent with this diagnosis.

Acute Transverse Myelitis: Inflammation of a segment of the spinal cord, which can cause bilateral limb weakness, among other symptoms. The onset can be rapid, and it often presents with sensory symptoms as well.
Spinal Cord Infarction: A rare condition where the blood supply to the spinal cord is interrupted, leading to damage or destruction of spinal cord tissue. This can cause sudden onset of bilateral limb weakness.
Multiple Sclerosis: An autoimmune disease that affects the brain and spinal cord, leading to a wide range of potential neurological symptoms, including bilateral limb weakness. However, the onset is typically more gradual.

Spinal Epidural Abscess: A collection of pus in the epidural space surrounding the spinal cord, which can compress the spinal cord and cause neurological deficits, including bilateral limb weakness. This condition is medical emergency requiring prompt intervention.
Cauda Equina Syndrome: A condition that occurs when the nerves in the spinal canal are compressed, leading to pain, numbness, and weakness in the legs. It is a medical emergency that requires immediate attention.
Botulism: A rare but serious illness caused by a toxin produced by the bacteria Clostridium botulinum, which can lead to muscle weakness, among other symptoms. The diagnosis might be considered if there's a history of ingestion of contaminated food or a wound infection.

Neuromuscular Junction Disorders (e.g., Myasthenia Gravis): Autoimmune diseases that disrupt the communication between nerves and muscles, leading to muscle weakness. While they can present with limb weakness, the pattern of weakness often fluctuates and worsens with activity.
Inherited Neuropathies (e.g., Charcot-Marie-Tooth Disease): A group of disorders that affect the peripheral nerves, leading to progressive muscle weakness and atrophy. The onset is typically gradual and begins at a younger age.
Toxic Neuropathies: Exposure to certain toxins (e.g., heavy metals, certain drugs) can cause peripheral neuropathy, leading to bilateral limb weakness. The history of exposure would be crucial in suspecting these conditions.