Compassion fatigue is a plain name for a real tiredness: you have been close to suffering, and your body has not caught up with the fact that the session ended. It can look like numbness, irritability, or a heaviness that follows you to the car.
After Session does not measure that, and it does not use a published burnout inventory. It offers a few minutes of paced breathing, a short body scan, and a place to set down a sentence. If the heaviness you mark stays high for two weeks, the page suggests supervision, a peer, or your own counselor. That suggestion is not a diagnosis.
If you are in crisis, contact local emergency services. In the US, the 988 Suicide & Crisis Lifeline is available by call or text.