Gerbil,
I have often thought stress is a big culprit in lengthening the healing and bringing back the symptoms. Anxiety is really the evil deamon! I do not think it is the reason why, PCS comes on but I think that it delays and worsens the symptoms. When my son is happy and with friends and family loving life, he is well. If he was stressed and exhausted all the time, I am certain he would regress in his recovery. Stay optimistic and preoccupied with what is good in your life and this may help.
Nancy F