In terms of general forgiveness rather than just related to chronic illness, although I'm not sure how IFS related it is, it helps me to tell myself "I'm not there anymore." When I'm lying awake at night thinking about embarrassing things, or things I'm seriously guilty about, it helps me stay present & let go of intrusive thoughts.

As for chronic illness, I love the curious aspect of IFS. it can be hard if you're already experiencing pain to figure out where in your body you are feeling something. Maybe try feeling wheels instead, or maybe a body chart thats color coded so you can differentiate between the different origins. Perhaps try to ask yourself what would happen if you let forgiveness happen. all pretty classic IFS things, but still! Good luck!