I agree with the other posters. As a child social worker, I have seen many cases similar to this. You may wish to speak with a therapist about what may be the underlying causes of this anxiety, and possibly to get him medication. I am not a strong fan of medication in some cases, but this sounds like a good case for there use.
Please take this very seriously. I had anxiety (still wont call it a disorder), but it ruined two years of my life. thank goodness i was in my mid twenties when it happened and as soon as the pain and worry got too much to handle and i was sleeping constantly and thinking of suicide when death has alwasy been my greatest fear, I got help. the meds helped quickly, and I was fully back to normal in about 5 weeks. Please help him. he does not feel good! he is hurting bad. i could not imagine having this at 8 and trying to deal with it. Please find him a doctor and get him some good meds to make him feel better. you sure dont want him to get worse...and trust me, by the day it gets worse!
Who else in the family worries, could he be picking up the talk and vibes from you or your husband ,any other close family member he spends time with, very often children learn a behavior by seeing and hearing it .
I suspect you are seeing the beginning signs of GAD - generalized anxiety disorder. Often, this disorder tends to "rear its ugly head" about the age of your son. Anxiety disorders are an inherited trait so there is nothing you can do to prevent it nor did you cause it. I might suggest you first educate yourself about this disorder by googling the phrase "GAD and children" or "anxiety and children" or similar words/phrases. If you feel this might be the issue with your son, then contact your family doctor for help. If he/she is unable to help you, then ask for a referral to a medical specialist with experience in anxiety disorders as a child psychiatrist or child neurologist. If anxiety is the issue, I assure you that your son will not outgrow it nor will it go away; but with proper treatment, he can learn how to manage his fears (irrational though they may be) and lead a very "normal" life. This is a very common mental health issue with children and highly treatable. I wish you the best ....