(I don’t experience any severe chronic pain, so if I’m completely off the mark with any of this, feel free to correct me.)
Someone with intense back pain might have difficulty getting out of bed. They probably could get out of bed, even if in pain, but most people wouldn’t expect someone to push through that kind of agony unless there were pressing matters to attend to.
Some people with intense pain can’t even bring themselves to go to work every day (or at all, in some cases).
If they do go to work, they might be tired and/or sore enough to be unable to do dishes, laundry, or other house work when they get home.
Chronic pain comes and goes, and sometimes it’s more debilitating than others. One day might be bearable and the next day, even going to sit at the computer is a task of unimaginable difficulty.
It seems as though, by and large, these things are accepted and the person experiencing the pain is not shamed for not being up to the tasks before them. Unfortunately, some people do experience invalidation from others, especially if the pain is not the direct result of an injury. Then, it’s “just in their head.” Which is pretty much the attitude toward depression and other forms of mental illness.
The thing about depression is that it is painful at times. Emotional agony is just as real as physical pain. At the end of the day, it’s all just brain signals, and most people have a pretty firm knowledge of what feels good and what feels bad, whether skin sensations or states of mind.
Depression, like chronic pain, can go for periods of time in “remission,” can pop up for a couple days at a time or months on end, and can be triggered by other things. Someone with back pain might twinge something while lifting a heavy object and be stuck in bed for several days. Meanwhile, someone with depression might have a particularly stressful day at work or a heated argument with a friend or partner, thus cascading them toward depression even if they were feeling okay beforehand.
They’re both unpredictable. They’re both painful. And they’re both real. Invisible illnesses deserve as much respect as cancer or Ebola. (Though you can leave the panic at home.) Nobody should face stigma just because they’re sick.