Kon, my older son has SPD (sensory processing disorder) and general anxiety. He was diagnosed in 2008 and is receiving therapy. My younger son seems to have it too, but more mild. I've also seen sensory issues in myself. From what I've read there is a hereditary link.
My older son is an avoider/defensive (hypersensitive) for the most part and my younger son is mostly a seeker (hyposensitive). I often describe it as my older son has his volume up too high, so everything feels too loud, too bright, too much. My younger son has his volume too low, so he needs to go faster, louder, harder to feel anything. He craves those sensations.
My older son would punch someone who lightly brushed by him because to him it felt like an attack. He would scream like he was being stabbed when he got sun in his eyes as a toddler. He would have meltdowns from unexpected loud noises. Now it's normal for me to tell him, "I'm going to turn the vacuum cleaner on now. It's going to be loud." Then he's fine.
My younger son loves big bear hugs, being squished between couch cushions, he likes sitting on my lap and twirling my hair, he prefers to eat all his food with his fingers.
People who are always clumsy probably have SPD. The proprioceptive sense lets us know where we are in space and where your body parts are. I definitely have issues with my proprioceptive sense. I don't quite make it around corners and will bump my shoulder on the wall. About two weeks ago, I just broke our table lamp because I moved my hand to turn it off, but instead bumped the whole lamp over and didn't catch it in time before it smashed on the floor.
I go to this website first for any questions I have: http://www.sensory-processing-disord...checklist.html
A lot of kids with SPD also have anxiety. Almost all kids/people with autism have SPD, but not all kids/people with SPD have autism.