One condition that occurs typically in lesions above the T6 level is autonomic dysreflexia (AD), in which the blood pressure increases to dangerous levels, high enough to cause potentially deadly stroke. It results from an overreaction of the system to a stimulus such as pain below the level of injury, because inhibitory signals from the brain cannot pass the lesion to dampen the excitatory sympathetic nervous system response. Signs and symptoms of AD include anxiety, headache, nausea, ringing in the ears, blurred vision, flushed skin, and nasal congestion. It can occur shortly after the injury or not until years later.