Will my impossible goals harm me physically?

I have 2 autoimmune diseases and stress is a known trigger. Brooke talks a lot about being comfortable allowing negative feelings and even says that if you’re not experiencing a lot of negative feelings, you might not be stretching yourself enough or you’re not growing and evolving. I’m trying to reconcile that concept with the idea that going outside my comfort zone always leads to anxiety which then leads my body and brain to produce stress hormones and chemicals, which could then trigger a flare of one of my diseases or even a new one. Any thoughts would be appreciated!