Sensory Integration Disorder--what is it?

Of course, even before seeing the therapists, I was on the internet all the time typing in key words trying to find out what was wrong with MJ. I would type in "walk on toes" and "sensitive to textures" or "afraid of heights" and out of everything, this is what I was coming up with--something called Sensory Integration Disorder.

So kids with this have some sort of extra need for like an over stimulus amount of sensory, like they may spin a lot or need to be moving all the time.

OR,

They may have this extra sensitive thing going on that everything is TOO much for them, like they can't handle the way things feel or taste. Well, not taste, but the way the food feels in their mouth. Or they are overly afraid of jumping or climbing or touching things.

Or it can be a mix of the two--an over sensory need AND an over sensitive thing.

This is what made sense with MJ. He could eat foods mashed up--like he would still eat baby food veggies, but if it was the chunks and real, he couldn't handle the texture. He freaked out if anything got on his hands or made him dirty. He couldn't handle tags on clothing, or if his pants or socks weren't perfectly stretched out touching his skin. And then of course he was 3 years old and he had never even been down a slide or swung on a swing really because it frightened him so terribly much.

But really---was this thing even REAL? Or did someone just make it up? It all sounded crazy.