There is a lot of information in the ES Information tab at the top of the page with information on why dizziness occurs.
One part in the ES Information tab talks about dizziness:
Symptoms common with Vascular ES are dizziness, weakness, or fainting (syncope). The styloid process is located between the External and Internal Carotid arteries, so if it is angulated, it can compress either of these. The stylohyoid ligament, if compressed, can aIso compress the arteries. It is possible that compression of the External or Internal Carotid arteries could temporarily cut off part of the blood supply to the brain, leading to a temporary loss of consciousness. Many people have found turning or moving their head into a certain position causes this, as this can move the styloid process or calcified ligament and so compresses the artery. In addition, pressure on these arteries can irritate the sympathetic nerve fibres in the artery walls, and this can send pain signals all along the artery. The ICA branches to the Ophthalmic artery, so if blood flow is reduced to this, there will be eye pain, and vision problems. Research states that if the ECA is compressed, pain is in the infraorbital (below the eyeand to the side of the nose), temporal, and mastoid regions (below and behind the ear). If the ICA is compressed, then pain is in the ophthalmic area (E.Beder, Ozgursoy, Karatayli: Current Diagnosis and Transoral Surgical Treatment Of Eagle’s Syndrome). And also ‘Hence, if the external carotid artery is affected, the patient may complain of pain in the neck on turning the head, or pain radiation to the eye, ear, angle of the mandible, soft palate and nose. When the internal carotid artery is involved, pain over the entire head and larynx may be involved.’ (Correll RW, Jensen JL, et al. Mineralization of the stylohyoid-stylomandibular ligament complex. Oral surg Oral med Oral path 1979.) Pressure on the ECA can also contribute to jaw pain. . Dizziness could be caused by compression of the Hering Nerve, which is a branch of the Glossopharyngeal Nerve, and connects to the carotid sinus to help regulate blood pressure. Also if there is compression or irritation of the carotid sinus- the area just before the carotid artery splits into the ECA and the ECA- this can affect the vagus nerve, and through the parasympathetic nervous system can affect blood pressure and heart rate. (see the link to R.B.’s post in the next section.)
The symptoms if the Jugular veins are compressed are slightly different. Because the veins take the blood flow from the brain, any compression of these interrupts the blood flow coming from the brain, and so therefore can increase the pressure in the brain (Intracranial Pressure- ICP). ). Over a long period sometimes other veins can compensate and take the blood flow away (‘venous collateral drainage’- Callahan et al). If the pressure in the brain increases, this is known as Intracranial Hypertension. Symptoms of this are also dizziness, plus headaches, tiredness, slow or confused thinking (brain fog), feeling of pressure or pulsing in the head and neck, feeling of pressure in the ears, pulsatile tinnitus (hearing heartbeat, often a whooshing sound), feeling generally ‘out of it’ or off-balance. It can also cause other neurological symptoms such as feelings of falling, or feelings of pressure on the head ‘like you’re wearing a hat’.
This is from an article I found:
The most complex and worrisome symptoms of Eagle syndrome are dizziness and eye pain. These may be caused by carotid artery involvement due to the carotid canal's location medial to the styloid process. An elongated styloid process with a thickened, ossified stylohyoid ligament could compress the artery and result in ischemic consequences such as near-syncope and eye pain. Since the internal carotid artery is a main vascular supply of the brain, its compression has dire consequences. The ophthalmic artery, the first intracranial branch of the internal carotid artery, is at risk of compromised flow in the event of internal artery compression. Ischemic eye pain and visual changes may result in these instances. The patient's dizziness may also have resulted from compression of the glossopharyngeal nerve through compromise of its carotid body nerve branch (the Hering nerve). Furthermore, pressure on external carotid artery branches may result in claudicant jaw pain and contribute to eye pain via altered flow through anastomotic branches of the internal carotid artery.