The painbody awakens when it feels hungry and it is time to replenish lost energy. But also an event can trigger it at any time. The painbody that is about to feed can use the most trivial event to trigger its appetite, from something someone says or does, or even a thought. If the person lives alone or no one is around at the time, the painbody feeds on the thoughts.
From one moment to another, the thoughts become deeply negative. The person was surely oblivious to the fact that just before the torrent of negative thoughts a wave of emotion invaded their mind in the form of a heavy black mood, anxiety or anger. All thoughts are energy and the painbody proceeds to feed on that energy. But not just any thought serves as food. It is not necessary to be particularly sensitive to notice that a positive thought generates a different feeling than a negative one. Although it is the same energy, it vibrates at a different frequency. A happy and positive thought is indigestible for the body of pain, which can only feed on thoughts compatible with its own energy field.
All things are vibrating energy fields in constant motion. The chair on which we sit, the book we hold in our hands seem solid and inert only because that is the way our senses perceive the frequency of their vibrations, that is, the incessant movement of molecules, atoms, electrons. and the subatomic particles that, as a whole, make up what we see in the form of a chair, book, tree or body. What we perceive as physical matter is energy that vibrates (moves) in a certain range of frequencies. Thoughts are made of the same energy but vibrate at a higher frequency than matter, which is why we cannot see or touch them. Thoughts have their own range of frequencies: negative thoughts are at the bottom of the spectrum, while positive thoughts are at the top of the scale. The vibrational frequency of the painbody resonates with that of negative thoughts, which is why it can only feed on them.
The usual pattern by which thought creates emotions is reversed in the case of the painbody, at least initially. It doesn't take long for the emotion of the painbody to take over the thought, and once that happens, the mind begins to produce negative thoughts. The voice of the mind begins to tell stories of sadness, anguish or anger about life, about ourselves, about other people, about past, present, future or imaginary events. The voice blames, accuses, denies, imagines. And we fully identify with what the voice says and believe all its distorted thoughts. It is the moment when the addiction to unhappiness takes over us.
It's not so much that we can't stop the negative train of thought, but that we don't want to. This is because, at that moment, the painbody is living through us and supplanting our true selves. And to the body of pain, suffering is pleasurable. Eagerly devour all negative thoughts. In effect, the voice that usually speaks in the mind has become the voice of the painbody and has taken over the inner dialogue. A vicious circle is then established between the body of pain and thought. Each thought feeds the painbody and the painbody, in turn, generates more thoughts. At some point, after a few hours or even days, once it is satisfied, the painbody goes back to sleep, leaving behind a depleted body and a body much more susceptible to disease. It looks a lot like a psychic parasite, which it really is.

(A New Earth, Eckhart Tolle)