There are many contributing factors to stress during the holidays without even including family. It can be a hectic time and many of us have to shift our environments, stepping outside of our everyday norms and out of our comfort zones. If you feel added pressure or anxiety from family gatherings, this is helpful article.
I talk a lot about mindfulness which can be a conscious technique for stress inducing interactions and establishing boundaries. How so? Listen to your body, for one. Be aware of how particular environments, people or circumstances are impacting you. Self-awareness is good for both anxiety and boundaries because you can then respond accordingly. You may find your heart racing, for example, indicating what is likely anxiety. For those who struggle with anxiety, you may already have techniques to aid with the discomfort. It's good to be prepared.
If you are a house-to-house type of person on Thanksgiving (or any other holiday), it can be overwhelming. You may have a large family or perhaps you receive several invites. Whether you feel obligated or happy to attend, there is only one of you. Setting time limits is a healthy and simple example of a boundary, both for yourself and others. Let them know you are spread thin and that you cannot stay for hours even if you would like to. It's good internal work because you can avoid over-exerting yourself, which is an example of you actively engaging in self-care. You have to practice setting boundaries so that it can become a norm. I suggest taking a moment for yourself on such a busy day, such as baking your favorite dessert (something to look forward to if you can't get away), swinging by your favorite park for quiet time, or going for a walk. Even a midday nap. It gives you a chance to re-gather or decompress.
Another good way to mentally prepare is to know your environment. If you know you're walking into a toxic environment, it's okay to prepare an exit strategy. No judgement. Being direct takes practice and can be problematic with some families, something you may not want to deal with on a hectic day. But saying NO is also powerful. Saying "I can't make it this year" because you feel it's a healthier option, is an ultimate mental health check. Assess yourself and determine if you can take it on.
If you're able to take a week long vacation with family, you're not likely getting much time for self-care or relaxation. That's not an assumption that all families drive each other nuts, but your norm has been disrupted and it is still healthy to check in on YOU. For everyone else, it may just be a hectic Thanksgiving or Christmas Day, consisting of tough interactions even if there's fun involved. It can be an overload, especially considering the eating and socializing which can easily lead to exhaustion.
Boundaries can relate to anything; personal space, energy, time, emotions, values, intuition, accountability, privacy, personal possessions; whatever is important to you.
I don't want to endorse suppressing one's feelings or hiding from family traumas. You're setting boundaries, not barriers. We have to deal. But there is a time and a place. Setting boundaries is about overall well being, establishing limitations with others (and yourself), not accepting any type of energy, maintaining healthy relationships, or sometimes just to feel safe. There are some things we can't control. Setting boundaries isn't one of them. It's a form of self-love. If someone is having a hard time, having compassion is obviously understandable, but there does not have to be a "sorry" involved every time you express yourself. Direct is best but you can judge the situation accordingly. There are other times when boundaries won't need expression, just action of self-prioritizing or practice.
We need boundaries in any environment. We practice them without question at work (most of us anyway), so why not in our personal lives? Here are a few articles on how to practice healthy boundary setting with family and how it can impact your health.