Benign Exertional Headache or Lightheadedness: This condition is often associated with sudden changes in posture, which can lead to temporary alterations in blood flow and pressure within the cranial vessels, resulting in a popping sensation. The blood pressure of 134/89 is within a relatively normal range, especially considering the context of possibly being a non-hypertensive patient, and the sudden movement could temporarily affect blood distribution and pressure.

Orthostatic Hypotension: Although the blood pressure is not particularly low, orthostatic hypotension can occur even with blood pressures that might be considered in the normal range, especially if the patient is not accustomed to sudden changes in posture. The symptoms can include lightheadedness and possibly a sensation that could be described as a "popping" due to the rapid change in blood flow.
Vasovagal Syncope or Near-Syncope: This condition is characterized by a sudden drop in heart rate and blood pressure, often triggered by stress or sudden movements. While the blood pressure provided does not indicate hypotension, the context of standing up suddenly could precipitate a vasovagal response, leading to symptoms that might include a popping sensation in the head.
Migraine or Tension Headache: Sometimes, the onset of a migraine or tension headache can be associated with unusual sensations, including popping or clicking sounds in the head. These conditions can be triggered by various factors, including sudden movements or changes in posture.

Subarachnoid Hemorrhage (SAH): Although less likely given the description, SAH is a critical diagnosis that cannot be missed. It typically presents with a sudden, severe headache (often described as "the worst headache of my life"), which could potentially be preceded by a popping sensation if the hemorrhage is related to an aneurysm rupture. The blood pressure might be elevated in response to pain.
Cervical Artery Dissection: This condition involves a tear in the lining of one of the arteries in the neck, which can lead to a stroke. It might be preceded by a popping or cracking sound in the neck, followed by headache and possibly neurological symptoms. Given the potential for severe consequences, it's crucial not to miss this diagnosis.
Temporal Arteritis: This condition, also known as giant cell arteritis, can cause sudden, severe headaches and might be associated with unusual sensations in the head. It's more common in older adults but should be considered, especially if other symptoms like jaw claudication or visual disturbances are present.

Patent Foramen Ovale (PFO) or Other Right-to-Left Shunt: In some cases, a PFO or other right-to-left shunt could potentially lead to unusual sensations, including popping sounds, due to the abnormal flow of blood between the atria. However, this would be an uncommon presentation.
Chiari Malformation: This is a structural defect in the cerebellum that controls balance and can cause a variety of symptoms, including headaches and unusual sensations in the head, especially with changes in posture. It's a rare condition and would typically be associated with other neurological symptoms.