Idiopathic Epilepsy: This is often the most common cause of new onset seizures in individuals without a clear underlying cause. It is a diagnosis of exclusion, made after other potential causes have been ruled out.

Traumatic Brain Injury: A history of recent head trauma can lead to seizures, even if the initial injury seemed minor.
Stroke or Transient Ischemic Attack (TIA): Seizures can be a presenting symptom of a stroke or TIA, especially in older adults.
Infections (Meningitis, Encephalitis): Although the question specifies "without fever," it's crucial to consider infections, as some cases may not present with typical symptoms like fever.
Substance Withdrawal: Withdrawal from substances like alcohol or benzodiazepines can cause seizures.
Metabolic Disorders: Electrolyte imbalances (e.g., hyponatremia, hypocalcemia) or other metabolic issues can precipitate seizures.

Central Nervous System (CNS) Tumors: Although less common, CNS tumors can cause seizures and are critical to diagnose early.
Cerebral Venous Thrombosis: This condition can present with seizures and is often associated with specific risk factors like pregnancy or oral contraceptive use.
Intracranial Hemorrhage: Any form of bleeding within the brain can cause a seizure and requires immediate medical attention.
Status Epilepticus: If the seizure is prolonged or recurs without full recovery in between, it's considered status epilepticus, a medical emergency.

Autoimmune Encephalitis: A group of conditions that involve an autoimmune response targeting the brain, which can cause seizures among other symptoms.
Mitochondrial Disorders: Rare genetic disorders affecting the mitochondria, which can lead to seizures as part of a broader spectrum of symptoms.
Vasculitis: Inflammation of the blood vessels in the brain can cause seizures, though this is relatively rare.
Parasitic Infections (e.g., Neurocysticercosis): In certain geographic areas or in individuals with specific exposure histories, parasitic infections can cause seizures.