Dear Dad - I feel for you that you are wit's end and scared stiff with what is going on with your son. I have six boys, and my eight year old has inherited my anxious tendancies, although they do not seem to be as extreme as your son's.
All the advice I have ever been given is to love him as you love the other kids (if you have other kids) and help him to learn to cope with his anxiety.His (and your) goal should be to cope with it , because it may not go away in all circumstances and he needs to learn to live with it.
For example, I am a youth minister at our church. Once a month, I have to walk down the aisle to the front of the church with the priest (after the entire congregation of about 1000 people has assembled) to lead all the kids to our Sunday School room. My 8 year old would never do that because he "didn't like being in front of all those people", so he used to wait in the back with my husband. After a while, however, we got tired of having our family separated for the first half of our church service, so we asked our son to "try it". He made it, holding tightly to our hands and with his little heart racing. Now, after several months, he has progressed to walking in between his older brothers, in front of us. Now, if we had asked him and he had been truly unable to do it, not even try to do it, I probably would have consulted the doc.
I guess what I am trying to say is, make sure you give your son an opportunity to accept and live with his anxiety (ie- no shipping him off to Grandma's because he dislikes you looking unfamiliar) because that is what he is going to have to learn to do, as have I and my 8 year old. If he truly can't adjust with you kindly and lovingly supporting him, I would take him to his pediatrician.
Please don't be scared, because I know that there are lots of good therapies and medications out there to help kids with anxiety. It may be a simple road to "recovery" like challenging your son and yourself - that is sometimes the hardest part for us parents right?

or it might involve therapy or even meds. ( I take them, but my son does not need them right now), but that's ok. He is still your lovely son, and now matter what, anxiety can be treated and you and your wife will still be able to enjoy your family. Sounds, too, like you must be close with extended family - what a blessing! Keep your chin up Dad, and remember, you and your wife know your little guy better than anyone, if you think he needs help, he probably does, so go out and get it for him, then you don't have to worry anymore -you can just enjoy life with God's greatest blessing - your child (or children!)
Keep posting! Best wishes, Marirose