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.