I also have chronic pain and anxiety. The most effective way I have found to manage the anxiety is to have a plan. Not a touring plan, but a plan for what possibly to do for each thing that I am worried about. AND then give myself permission to not follow the plan if it no longer works for me!
My brain is an expert at "what if's", so here are some examples:
What if I get high pain and exhaustion in the middle of the day? I will schedule enough days in my trip that I can go back to the hotel for a couple hours mid-day and still leave time for doing all or most of what I want to do. I will consider lying down at first aid for awhile.
What if I hurt so bad that I am sick and can't help myself? I will arrange ahead of time with a member of my group that they will help me get back to my room.
What if in the middle of a cue something bad happens? I'll ask a cast member for help (remember-self, they are nice and helpful). I'll leave the cue. I'll try again later.
What if two days into the trip I just can't do anymore and need to recover? I planned for a rest day at day two or three. I planned all the intense things in the first day or two so that if this happens (as it often does) I can do things extremely slowly and leisurely the remaining days. Before we go I identify the activities that I will likely enjoy that won't hurt me, a show, a parade, a slow ride, and then I plan to do that if I hurt and really focus on taking in all the details.
We are going to
Disneyland/DCA in Feb and we will be there 7 days with a 5 day pass. This leaves lots of wiggle room to accommodate unexpected challenges, and lots of time to make up for a lost day. I'm also doing my best to avoid planning ANYTHING for the week or two after we get home so that I can recover.
I spend a lot of time prioritizing which attractions are must see, which rides are likely to hurt but I still want to do ONCE, and which things I will be kind of ok with missing. And I read books and guides that describe things to do at Disney that aren't rides. So for me I know that I love Indiana Jones ride but it hurts me, so I will plan to go on that either right before nap time or right before we leave the park, probably the evening before rest day, giving me time to recover. Being cold and wet is BAD for me, so I will do wet rides right before we leave for the evening and/or bring dry clothes. If I need an extremely slow and easy day I will look for the hidden Mickeys, or go on a treasure hunt for interesting details (can a find a light bulb painted two colors? Take a picture of each bronze statue). I want to second that "small goal" idea as well. And I remind myself that it is completely acceptable to not see and do everything!
For me writing down my worries is a big help for putting anxiety in check. And makes it easy to go back and look and get some idea of how to overcome that obstacle. Focusing on the solution can reduce anxiety.
For making the best of a trip when I'm in pain I pack with me things that comfort me and help ease my pain. For me that looks like: a small crochet project, a word puzzle book and pencils, something super soft (a blanket, shirt, pjs), my heating pad for at the hotel, my instant heat packs for in the park, my favorite ice pack, my favorite topical (tiger balm), a good book. At home I try to minimize the amount of medication for pain that I take. In the parks I will take meds on a schedule in hopes of staying ahead of the pain, because pain is much easier to prevent than to chase away after the fact. I try to focus on the positive. For me, I can deal with a lot more pain if I am doing sometime I fun, so I remind myself of this. I will put alarms on my phone to remember to eat take meds regularly, my pain skyrockets when I forget to eat. I also bring what is for me a ridiculous amount of shoes (I'm not a shoe fan). I'm not talking fashion shoes either. I bring my best walking shoes, my comfy ugg style boots that I wear as slippers, my flip flops for the pool, hiking boots - because sometimes they help, my hiking sandals, maybe a second pair of walking shoes because sometimes changing helps. I spent some time convincing myself that the extra expense of some of my strategies is worth it to have a good trip. And I saved up and budgeted for it. Yes, I will need a locker every day. Yes I will need to pay for the extra suitcase for the shoes and heating pads and other comfort items. Yes I need the bigger room with the kitchen. And yes, I will need to rent the ECV the whole time, and that's ok.