explaining why you miss parties

This is a very good question, I have tried different things and I struggle with an answer, If I just don´t show up everyone used to ask why is she becoming unsociable, then I decided to take the long way explaining that htere are ggod days and bad days and that must of all I like to avois strenouss activities so that i avoid having bad days for a month, but my extended family forgets all about it the next time Im not there, the really really sad thing is what happens with my brother, he knows exactly about my conditions (I am endo warrior as well) but everytime there is anything stressful to do with our family and he wants me to be part of it and i say with honesty how I want to avoid it as i dont consider necessary all the fuss because its not good for me then he says "You must stop taling about your health and thinking averything is bad for you"
I have been very thoughtful about pain and the feeling of pain lately, i hear everyone who doesn´t look like its having easy with pain, I respect anyone who says to feel pain I feel compasionate no matter how old the person is, the journey through pain is tough and none JUST NONE knows how much pain is the other fellow going thru. HAving said this, -i preffer now just not to say anything to anyone, doing for myself what I think is necessary and looking forward to the good days