Sudden cross eyed vision vision?

Could be many things: If this happens, see a doctor immediately. It could be decompensation of a pre-existing muscle balance problem. It could also be a stoke that can cause this, but less likely and far more dangerous. Again to sort this out, please have an exam.

Emergency: You should see an eye md immediately, this can be a serious emergency and could be deadly. There are many causes; stroke, carotid dissection, migraine, micro-vascular disease, brain tumor, brain bleed, diabetes, high blood pressure. See a doctor.