Multiple Sclerosis (MS): This condition can cause a wide range of neurological symptoms, including headaches, sensory disturbances (such as decreased sensation in the lower limbs), and potentially altered temperature perception. The variability and combination of symptoms can make MS a plausible explanation.

Hypothyroidism: Can cause feelings of cold intolerance, headaches, and neurological symptoms including numbness or tingling in the extremities due to its effects on metabolism and nerve function.
Vitamin B12 Deficiency: Leads to neurological symptoms such as numbness or tingling in the hands and feet, and can also cause fatigue, weakness, and cognitive difficulties. Headaches can be associated with the condition due to its effects on the nervous system.
Diabetic Neuropathy: In diabetes, high blood sugar levels can damage nerves, leading to decreased sensation in the lower limbs. It can also cause autonomic dysfunction, potentially leading to altered temperature perception and headaches.

Subarachnoid Hemorrhage or Other Intracranial Bleeds: Although less likely, these conditions can present with sudden, severe headache and, depending on the location and extent of the bleed, can cause neurological deficits such as decreased sensation. Missing this diagnosis could be fatal.
Spinal Cord Compression: Can cause decreased sensation in the lower limbs, and depending on the level of compression, can also lead to autonomic dysfunction, potentially causing altered temperature perception. Prompt diagnosis is crucial to prevent permanent neurological damage.
Multiple System Atrophy (MSA): A rare neurodegenerative disorder that can cause a combination of symptoms including autonomic dysfunction (leading to temperature regulation issues), parkinsonism, and cerebellar ataxia. It's less common but critical not to miss due to its progressive nature.

Adrenal Insufficiency (Addison's Disease): Can cause a variety of symptoms including fatigue, weight loss, low blood pressure, and changes in skin pigmentation. Some patients may experience neurological symptoms and cold intolerance.
Tabes Dorsalis (Neurosyphilis): A late manifestation of syphilis that affects the spinal cord, causing symptoms such as lightning pains, ataxia, and loss of reflexes. Decreased sensation in the lower limbs and altered temperature perception can occur.
Ehlers-Danlos Syndrome: A group of disorders that affect connective tissues supporting the skin, bones, blood vessels, and many other organs and tissues. Some types can cause neurological symptoms, including headaches and decreased sensation, due to the fragile nature of blood vessels and potential for spinal instability.