The author of http://www.sensory-processing-disorder.com/ does a wonderful job of helping us understand what it must be like to have SPD. Below I have a copied an excerpt from the site:
You could see obstacles in your way, but you could not make your body move the direction you wanted it to to avoid them.
You felt like someone had given you a shot of Novocain in your backside so you couldn't feel if you were sitting in the middle of your chair and you fell off 3 times during this training.
Your clothes felt like they were made of fiberglass.
You tried to drink a cup of water from a paper cup, only you couldn't tell how hard to squeeze it to hold onto it. So, you squeezed it too hard and the water spilled all over you. The next time you didn't squeeze it hard enough and it fell right through your hands and onto the floor.
Every time you tried to write with your pencil, it broke because you pushed too hard.
The different smells in this room made you utterly nauseous.
The humming of the lights sounded louder than my voice.
You couldn't focus your eyes on me because everything and everyone in the room catches your attention and your eyes just go there instead.
The lights are so bright you have to squint, then you get a pounding headache half way through the presentation
Every time someone touches you, it feels like they are rubbing sandpaper on your skin.
You could only sit here for 15 minutes and then you had to take a run around the building or do 20 jumping jacks so you could sit for another 10 minutes before your muscles felt like they were going to jump out of your skin.
People's whispers sounded like they were yelling.
The tag in the back of your shirt makes you feel as uncomfortable as you would if a spider was crawling on you and you couldn't get him off.
You wanted to write something down but it took you at least 5 seconds to form each letter. You can see the letter in your head, but your hand will not go in the right direction to write it.
You had to pull the car over 3 times on the ride here because the motion makes you sick.
These examples may sound extreme but for some with sensory processing disorders they are not.
This sounds so scary to have to deal with everyday, yet my little girl does so bravely. It is soooo important to put ourselves in her shoes.