The only physical activity I could do was walk, slowly, preferably outside.

I downloaded a lot of guided relaxation and meditation podcasts and listened to those. I also listened to nature sounds (rain, waves, etc) while lying in a dark room. It gave me something gentle to focus on.

I also found coloring to be helpful. At the beginning, I had to do very simple pictures where I didn't have to think too hard about what color to make things. Now I'm able to do some slightly more complex designs.