what is an invisible illness? and how do society treat it?

An invisible illness is something that effects people and they never get noticed by it by others because it is something that you can’t really show if that makes sense or only if you say something about what you have. Sometimes the invisible illness is so invisible that when people that have invisible illness park in a handicap spot people would say something like “you’re not disable, when they really are but its invisible. Society also treats it like its something that can get better in the future when really sometimes it can’t get better and that what they are gonna have to be doing. Also another thing is that society thinks just because they are okay the other day but then that person isn’t the next day, they don’t understand that mental illnesses can change your mood every second, minute, hour, or even day. But society treats invisible illness like nothing really because it can be so invisible they won’t even notice at all, and just think you are okay when in reality you really aren’t, and people aren’t understanding.