Well that's horrifying

Hopefully she hasn't passed anything onto you. If you start experiences some strange symptoms, such as seeing the strange man or just knowing that he is around you, try signing up for a sleep study. Or recording yourself. Try getting a brain scan, and, on that note, check what was on your mother's brain scan. It could disprove this shadow man or clue you in on what he is.

And as horrible as it may seem, if you have inherited the shadow man and cannot find a way to stop him, you may want to incapacitate yourself in a manner that would prevent you from passing him onto anyone else you may know. That means ensuring you cannot speak and maybe preventing yourself from forming coherent thoughts.