Congratualtions on the new job I am sure you will go fine, just don't stress yourself.
I returned to work after my surgeries and treatment and to be honest I struggled all of last year. I think I went back way to early but I felt my mind needed to be busy, trouble was it had holes in it.
I am extremely fortunate that my employer has shown empathy to my situation and undersanding to my need to attend appointments etc..
I found that if I stressed myself I seemed to have more holes, so I made it through by writing important thingings on my white board, using my calendar to my advantage and resting at the end of the day. I had to learn that I couldn't come home and do all the things I used too.
You will get there just be gentle on yourself along the way.
Donna