Migraine: This condition often presents with pressure or pain in the head, which can be preceded by or accompanied by other symptoms such as a cold chill or weakness. The combination of these symptoms, especially if they are recurrent, makes migraine a plausible first consideration.

Viral Infection: Many viral infections can cause a range of symptoms including headache, chills, and weakness. The onset of these symptoms could indicate the beginning of an illness like the flu or a common cold.
Tension Headache: While typically less severe than migraines, tension headaches can cause pressure in the head and may be accompanied by feelings of weakness or chill, especially if the individual is under significant stress.
Anxiety or Panic Attack: Sometimes, anxiety or a panic attack can manifest with physical symptoms such as a feeling of pressure in the head, chills, and weakness, alongside more typical symptoms like a racing heart or shortness of breath.

Subarachnoid Hemorrhage: Although less common, a sudden, severe headache (often described as "the worst headache" ever experienced) can be a sign of a subarachnoid hemorrhage, a life-threatening condition that requires immediate medical attention. The presence of a cold chill and weakness could be associated symptoms.
Meningitis: This infection of the membranes surrounding the brain and spinal cord can cause headache, fever (which might initially feel like a chill), and weakness. It is a medical emergency.
Stroke: A stroke can present with sudden weakness and sometimes headache. While chills are less common, the sudden onset of any of these symptoms warrants immediate evaluation for a stroke.

Multiple Sclerosis: This chronic condition can cause a wide range of neurological symptoms, including headache, weakness, and potentially sensations of cold. However, the diagnosis of MS typically involves a pattern of symptoms over time rather than a single episode.
Temporal Arteritis: This condition, which causes inflammation of the blood vessels in the head, can lead to headache and potentially systemic symptoms like fever or chill. It's more common in older adults.
Pheochromocytoma: A rare tumor of the adrenal gland that can cause episodes of headache, sweating, palpitations, and weakness due to the sudden release of hormones like adrenaline.