What causes the zig zag vision during a panic attack?

Like a migraine: It's probably due to increased neural activity in the visual cortex of your brain.

Ocular migraines!: Ocular migraines are a form of migraines that take place in the occipital cortex (part of the brain that interprets/controls vision). They lack the severe headache as common migraines. The symptoms are usually all or mostly visual and are typically described as flashing of light or ziz-zag lights in the vision. They usually last less than 30 minutes and affect the vision out of both eyes.