I try to think about how my body reacts to being terribly ill...like a bad upper resp. infection or stomach flu...basically, whenever you are trying to heal, and you do stuff that your body would rather you didn't because it is busy trying to heal, it gives you signals. For me, it tends to be chills/cold sweats, headaches or just random pains in my forehead and temples, and weakness/exhaustion. When I go too far and I get a bad headache, it feels like a wound opening up in my brain...sounds dramatic, but I think that's basically accurate; I'm essentially re injuring myself.