A blocked carotid artery usually has no symptoms in its early stages, according to Mayo Clinic. Once the blockage is severe enough to deprive the brain of blood, the patient experiences a stroke or a transient ischemic attack.
Strokes and transient ischemic attacks can cause sudden dizziness or loss of balance, sudden trouble speaking or understanding, and sudden trouble with vision, reports Mayo Clinic. A sudden, very painful headache without a known cause or sudden weakness in the face or limbs may also signify a blocked artery or stroke. A person with any of these symptoms should consult a physician.