That's an interesting take.
Take my Myasthenia though. It's not psychological in origin. What happens is that exercise triggers an attack on the neuromuscular junction . The more we move the more the muscle receptors are attacked. This means less nerve signal can get through to our muscles so we get increasingly weak.
The main variable that influences my symptoms is how much I move. So I tend to be strongest first thing in the morning and weakest in the evening. Heat also affects it hugely. So I can barely walk in this heatwave, but when I got into a cool pool I was able to swim for a while. The traditional test used to be an ice pack test- if ice pack is applied to a droopy eyelid the eyelid will spring back up. I keep cold eye masks in the freezer to help with my weak eye muscles in summer.
Stress can affect symptoms too, eg when my relative died I became so weak I couldn't swallow within minutes of hearing the news. Hormones can affect it to - my symptoms are worse just before and during my period. But none of these mean it is a psychological based condition. I can be very weak during periods when life is easy and relaxed, because a cold will make it flare or if I do too much exercise that makes it flare.
It's not actually invisible either. My family can tell because my eyelid droop (ptosis) gets worse when I am flaring. But most people aren't going to notice that.
And my point is, that people battle all sorts of conditions where their presentation may make no sense to a casual observer but make a lot of sense when you understand the science behind them.
My neighbours are used to seeing me now sometimes walking the dog unaided, sometimes with a stick, and sometimes in my wheelchair. To anyone with an understanding of my condition that makes perfect sense. Depending on the time of day, the time of the month, the weather, and what else I have already done that day my condition varies wildly