One of big keys for me being able to handle holiday stress is preparation. Not only reminding myself not to take on too much, but also thoughtfully reminding my friends and family of the difficulties I might run into. Sometimes a thoughtfully worded note reminding them that the holidays can legitimately cause some health problems for me can be extremely helpful in getting people past hurt feelings. Reminding them, that of course I want to partake in every activity and event, but that it simply may not be feasible. I like to mention that it's not me failing them, it's my body failing me and them. A little awareness goes a long way.
I also like to make sure that if I do go to a family function, that I stay aware of my body and try to have a room I can go take a timeout in. Sometimes laying down for a few minutes away from the hustle and bustle can be extremely helpful.