Autoimmune thyroid diseases can cause muscle and joint pain. In my experience, there is good and bad day, but all days have some degree of muscle and joint pain. Never assume that someone is not experiencing pain when they say they are fine. They might be able to function, but the pain is still there, and it still draining.
In Hyperthyroidism and Graves Disease, patients can muscle weakness and fatigue. White blood cell can actually attack part of the muscle and some surrounding blood vessels. In my case, I have to be careful with stairs as I have experienced muscle weakness and went tumbling.
I also struggle with picking up stuff on the floor, which is very frustrating. We can still do the things that cause us pain, but I have found that on those days where I push my limit, I am rewarded with a day or two of debilitating muscle and joint pain. Since I know pushing my limits is a trigger, I try to avoid doing so on Sunday or weeknights to ensure that I will be able to go to work the next day.
As recommended by my doctor, I am trying to do low impact exercises in order to help with rebuilding and strengthening muscles.