I always used to be anxious since I was a child. 
I was diagnosed cancer at 17 and got a 9-months treatment for it.
My anxiety disappeared, I always felt confident, social, I felt no pressure, no panic attacks, no overwhelming fear. I thought it was strange to feel this good mentally while I was suffering physically.
But the healing process brought me back to reality, my anxiety got worse and worse. The more my body was gaining strength and energy, the more my mental health deteriorated. 
At some point I even hoped for my cancer to return.

Is there any explanation for this thing it's happening? Why was healing so bad for me?

Note: excuse me for my grammar, English is not my native language.