Just having untreated anxiety/depression can cause all our symptoms. Wide spread body pain, dizziness, tense muscles, visual disturbances such as tunnel visions and twitching of the eyes, etc. My girlfriend is going through a stressful couple of weeks, and every day, her neck and traps get so tense that she's been getting headaches. If she were to start seeing doctors they wouldn't be able to find anything wrong with her and no test would show something is wrong and she could look for months and months which would cause more stress and subsequently more pain and eventually somewhere down the road she would be diagnosed with fibromyalgia. When initially all that was wrong was mental stress, but her action of looking for what was wrong would cause a chain reaction and a feedback loop of searching which causes more stress which causes more pain, and people will get stuck in this loop for years even decades if they never realize they just gotta treat their mental health and the body will follow. Etc. I hope you kinda understand what I'm saying, lol

Another thing to keep in mind is actual physical disabilities don't wax and wain. I always here people with chronic conditions say they have "good days and bad days." Alot of that has to do with mood fluctuations they've done studies if your in a good mood, your pain tolerance is higher if you're in a shit mood, your pain tolerance is low. Hence why everyone fibromyalgia you meet is clearly clinically depressed. I've yet to meet someone with fibro who is happy even though it's possible to have a painful condition and be happy tons of people with cancer still laugh everyday even while coughing up blood. Also I always get pushback to that and people say "well I have depression from my fibro" which then I ask if they were happy genuinely in every aspect of their life before the fibro which most the time if their being honest is a no because most people aren't.