ARG! Just wrote 2 screens and lost it!
Bear in mind that if you google sensory integration, you'll find lots of seemingly scary information. Sensory integration disorder is often found overlapping with autism and serious learning or developmental issues. HOWEVER, LOTS of kids who are well with the range of normal development have sensory integration issues - not a "disorder" that needs serious intervention, but some issues that need patience and help developing coping strategies. Sensory integration is the process by which your brain takes in all the information it receives through the five senses and figures out what to pay attention to and how to respond to it. For most people, this is all automatic and unconscious - it's how we know how loud to speak, how hard to push a car door to close it, how to pick up a coffee mug without throwing it, how to walk down stairs without looking. Through trial and error, our bodies figured this stuff out, and we dont' even have to think about it anymore. We tune out stuff that doesn't need our attention, and tune into what we should pay attention to. Oversensitive kids can't tune things out, so they can feel overwhelmed and easily bothered. undersensitive kids tune out a lot, so they seek stimulation and aren't easily bothered. But this system is growing and developing rapidly until like age 8-9, so there's lots of time to help a kid struggling in either direction to develop copoing skills.
Generally, a sensory issue is diagnosed by an occupational therapist and treated through occupational therapy (OT). Some kids aren't so severe that they warrant a "diagnosis" but can still benefit from OT. This is "play therapy" - things like hiding materials in a bin where kids can't see them and having them find them by touch (so they distinguish textures), games where they have to reach up high then down low (building balance and sense of body position), lifting or moving heavy items (like classroom furniture), excercises that help them develop a sense of their own body, speaking in soft voices, etc. Massage and gentle pressure to the body is often used (like a hand on the shoulder when talking). I know it seems weird, but these kinds of things help the children get lots of information to the brain about their bodies, and they kickstart the sensory integration process. A lot of it is stuff that can be made into a game, and can be done at home. I do some of it in my class of 3 year olds with all the kids, b/c they like it (we are hopping like frogs to the bathroom today)
I have a few students with SI issues (both ways) and I tell their parents that what i think is most important is that they help the child see what they need and ask for it so the kids can advocate for themselves (like my oversensitive kid asking for his space and using a napkin, so he doesn't freak out when someone touches him or his hand are dirty), and that the parent advocate for their child - b/c a lot of these kids get labeled as "behavior problems" when sometimes it's really about the kid having a hard time in the environment. It's better to understand it so you can help them cope. I hate the thought of a child being labeled as a "problem" in school when really it's because the particular environment sets them up to struggle and just a few changes make a world of difference.
Don't get discouraged - even if you think your child may have an SI issue, really that's just a label to help understand what's going on in a child's head and how to help them cope with the world so they can be successful. It doesn't mean they will be any less successful or happy than the next child, but may mean they need to be understood for who they are and help developing coping strategies. And again, i'm not trying to label your child based on just a few clues, just putting this out as an option to investigate. he may just be a super-extroverted chatterbox!