I'm 19:52 from this thread
http://www.dcurbanmom.com/jforum/posts/list/312006.page . From your brief post, I think it would be helpful for you to speak with a psychologist. We first noticed anxiety in our DS when he was about 4.5. He started avoiding social situations where he didn't know all the kids - and I mean ALL the kids. When we realized we had a problem, we spoke to our pediatrician who recommended a psychologist as well as an evaluation with a occupational therapist (OT). We were able to get an appt. with the psychologist first. The first meeting was with DH and I only. He took a case history, asked us lots of questions and suggested we first pursue the OT evaluation. If that didn't help, come back and see him. The OT evaluation was helpful, revealed DS had some motor planning/coordination issues as well as some emotional regulation issues that OT helped.
DS was always very sensitive, reacting much the way you describe when he didn't just shut down all together. Things got really, really bad as he anticipated starting 2nd grade. We were all miserable and I was pushed to my limit (and I'm really resilient). That's when we tried another psychologist and CBT. If you read the other thread you can get the summary. I do think you should start to address the issue now. Your DS may not need medication but the techniques he learns to help him control and change his emotional state are life skills that will benefit him his whole life. HTH