Help me explain to friends why i often have to cancel plans

I'm so sorry to see that so many others have this problem. Over the years, I have found that very few people can comprehend chronic pain unless they experience it. Tragically, this includes medical personnel!

I can say this with absolute certainty, because I was one of them. Even worse, I was working in a chronic pain clinic and helping to run a chronic pain program when I first started having problems!
School, and life, taught me that pain was transient. People have pain as a symptom that something is wrong. And,often accompanied by at least one of the 3B's (Burning, Bleeding, Breakage 😉) or as a direct consequence of them and generally there are visible signs. If someone looks fine, make sure there's "nothing wrong" internally, reassure and let them go on with their lives. And then there was the big, HUGE fallacy that we were taught was a universal rule: If people do therapies (PT, OT, TR, NeuroPsych, Aquatic Therapy and several others!) like they're supposed to and have a good team supporting them, pain is transient and survivable without ANY need for long term opiates, or drama. If someone breaks these rules, you start (compassionately!) looking at them for things like addiction, malingering, drug seeking, mental health issues, attention seeking, etc.
When I started having issues, I DID everything right. (I even thought I'd have a great story to encourage patients with! 😂). I saw ALL the specialists. I had ALL the tests. I attended therapies religiously and gave it my all. I took the non-opiate medications suggested. I iced, heated, soaked, wrapped, stretched, moved through, strengthened and got worse, even though none of the 3B's were obvious. I was suddenly a malingering, drug seeking, nut case that was depressed, bored with my life and wasn't getting enough attention.
I looked “young”, “healthy”, “beautiful”, “happy” and “fine”...
I took suggestions to "smile”, “just put it out of my mind”, “move forward”, “move on”, didn't “give it my energy”...
I accepted that I'm “not unusual or special”, “sometimes life is uncomfortable”, “pain tolerances are primarily based on perception” and “opiates mask symptoms and kill”.

What I'm getting at is that there is no perfect way to explain your reality to people. They get it or they don't. Some people will try harder than others to understand or think they understand and showing you patience and compassion. Others will tell you all those little encouraging quotes above and 100 common others, with a pure heart and the best intentions.

I've found that what works best for me is simply telling people the truth like you did here. Sometimes that means the whole story, sometimes it's a shortened version of some sort and to the rest I say, “Some days the best you can do is suck. I'm having one of those days.”
Something that does seem to work, possibly better than just telling people, is confiding in them. Remember, everyone wants to feel like a hero, allow them be yours! Let them be someone you can share your truth with. Let them help you as you soldier on. It benefits both of you and people tend to be so much more understanding/forgiving if they feel like they are part of what is happening and can do something about it.

Sorry, brevity is obviously not my strong suit. I really hope this helps!

@psychedancer THANK YOU! You have shared my husband's situation precisely. And from your perspective it means so much. He has suffered from chronic pain for at least 20 years and did all the things you described. Still, no one really understood. I want to cry for you, for him, for all who suffer this way but have been silenced. A nurse during one of his many hospitalizations once said said, compassionately, that she felt so bad for him. She said if you break a bone or have a wound people are so understanding and compassionate. But when they can't see your pain, they write it off. So true.

He has been fortunate to have friends who get it and that is a real blessing. They are his age, early 80's now, and either suffer with medical conditions of their own or have others in their life who do. That makes a huge difference.

I have a similar situation. Lately have not even attempted to attend any functions. My immediate family know of my condition, but it is not shared with others. Of course except here with no real personal info.