My mom, one sister, dd and I are like this. Maybe not enough to be "clinically" diagnosed, but definate tendancies. I did a quiz for dd, and aside from 2 questions that weren't age appropriate, the only sign she didn't have was sensitivity to clothes. She prefers soft clothes over jeans, but isn't fussy about socks or anything, and will wear her plastic dress up shoes until she gets a blister (girly!) It gets better with age.
With dd I feel like I have to be super vigilant about her feelings getting hurt, and I've tried to eliminate 'perfect' from our vocabularies. I point out my mistakes and laugh at them, and tell her that's one way we learn. I try to get her to talk about everything she feels.
She can be very hard to get to leave the house, because then she has so many new things to process.
I've encouraged her to take deep breaths, and count to calm herself. I also have a few little songs, and I get her to think of them, or sing or hum them, to give herself time to think. I know when I'm stressed, I retreat, so if we're going somewhere stressful, I'll bring something for her to focus on, like her leap pad, a book, or give her my phone to play with.
She is amazingly observent and perceptive, and I'm going to do my best to teach her to keep those qualities while learning to look at things objectively before she lets things get to her (to much).
I think a lot of it is the age. There's a lot going on. Recently or newly potty training, new foods, more independence/distance from Mom & Dad. The world is a scary place. My son is 11 and for a long time I worried about how fearful he was. I tried to down play it but it didn't work. So instead of battling over if he would try the slide, I told him he didn't have to. And I just let him do what he wanted to do at the park. Which was mostly just watch the other kids. He was the same way at daycare. We kept going to the park and to do other things but mostly he just sat and watched. One day he decided to give it a try I guess. He had just turned 5. Nothing horrible happened and he's been less reserved ever since. But he's a look before he leaps kid. And that's ok. Not at all suggesting that you shouldn't "do" something if you feel like you should. But maybe just try and let him dictate his path? And then be there to pick him up when he finally does allow himself to stumble? Or I could be completely wrong. Shoot... I'm no expert. I hope it works out for the best!