I've recently seen a number of signs on disabled toilet doors along the lines of "not all disabilities are visible".
This discussion has focused on wheelchairs (and yes, that was/is the subject line) but PRM covers a much wider range. Indeed "assistance" covers an even larger range and could ,for example, include interpreters (for language or sign language).
In my view we're only scratching the surface both in this thread and in what happens in life generally.