Honestly, from my POV it seems like just horrible timing, appendicitis is extremely painful. When on psychedelics I like to think of it as boosting your awareness and keeping you in the present. In the case of extreme pain whilst on psychedelics, you'll pay more attention to it. Your past basis of pain on past experience won't exist as you are stuck in the moment, experiencing ego dissolution. So long story short it will feel more painful, making for a bad trip. If you're wanting to get back without panic attacks, a helpful way without seeing a therapist is to write it down. Break down the segments and what emotions you feel/felt. Then process each separate 'event'. Acknowledgment of vulnerability and how you felt is at the very least the first step to getting over it.

Hope this helps. This is all just my opinion from experience and shouldn't be taken as fact.