I don't think living at home with your mom is necessarily unhealthy as long as you are carrying your weight financially and with doing things around the house. I think it's wonderful that you are so close. My son is your age and still lives at home though he pays some bills and supports himself. He suffers from depression and I am bipolar and my husband is perfectly emotionally healthy so my son and I are good support for each other.
As far as your mom not being around, 55 isn't very old. Enjoy each day with her - none of us can count on tomorrow!
Yes, you probably do need to relax but it's easier said than done.