I hit my head in the summer of 2013. up to now i've only had this feeling about 4 times of severe dizziness and a sense of dread. what could it be?

Go MD for eval: Symptoms depend on the type of head injury. Some severe symptoms may not appear right away. Mild head injury symptoms include: inability to stand or balance confusion headache nausea temporary memory loss ringing in the ear severe head injury symptoms include: bleeding from deep cuts or wounds in the scalp, loss of consciousness abnormal eye movements inability to focus the eyes.

Anxiety: It sounds like anxiety but it persists i would see a physician.