What if you wake up and you find out that your SO has forgotten everything?

Suppose you're with your partner. What if someday you wake up and when you talk to your partner, you realize that s/he has forgotten everything. Most of his/her memories has lost or has memories only from a specific period of life but not when s/he met you or his/her job or college. S/He forgets everything about you and your relationship. What would you do then?