Eckhart Tolle describes a Pain Body as being:
"the pain-body is every emotional pain that you have experienced which leaves behind a residue of pain that lives inside you:
“As long as you are unable to access the power of the Now, every emotional pain that you experience leaves behind a residue of pain that lives on in you. It merges with the pain from the past, which was already there, and becomes lodged in your mind and body. This, of course, includes the pain you suffered as a child, caused by the unconsciousness of the world into which you were born.”
So he goes onto suggest that:
"This accumulated pain is a negative energy field that occupies your body and mind. If you look on it as an invisible entity in its own right, you are getting quite close to the truth. It’s the emotional pain-body."
So in a nutshell, its all the trauma you have experienced in life that manifests Physically and Mentally. When I happened upon this information, I realized that maybe a good portion of my trauma has manifested itself Physically, since I am suffering from certain ailments. So This website:
https://hackspirit.com/eckhart-tolle-re ... epression/
Gave me an understanding of what to do have an "awareness" of this physical manifestation. So at the time, I was suffering from swelling of the legs and the doctors could not pinpoint the source of it. So I begin to ponder "What kinda of trauma has physically manifested in my legs?"
I realized that the trauma came from my emotional distress of not a having a car for a couple yrs and had to walk everywhere in which it was very emotional and physically taxing for me. I Remembered being upset alot of times during those walks and the long bus rides I had to take to and from places.
So I took the points from the website and begin to focus on my legs. I begin to talk to them, acknowledging the trauma and the pain I and what my legs went through. I would verbally tell my legs after my acknowledgement to release the pain and to never return. I did this for about 2 weeks non-stop. The swelling went away and haven't been back since. Its been 1 yr since I did that.
I hope that this helps everyone in their Journey towards Healing.

Sources:
A) https://hackspirit.com/eckhart-tolle-re ... epression/
B) Eckhart Tolle- "The Power of Now"