Scared/Biting

Question
Help!  Our 8 year old boxer is starting to bite.  We have had him since he was a puppy and nothing in our household has changed.  If anyone gets close to him, even just to pet him, he squeels like he is scared and snaps at them.  This happens when he knows they are there, meaning they are not suddenly scaring him.  

Yesterday at bed time our 18 year old daughter put a blanket on him and started to pet him, as we have done 100's of times in the past, and he bit her, drawing blood.

Today we were all in the Kitchen and my 14 year old son reached down to pet him and he snapped at my son, I watched the whole thing. If my son would not have pulled away quickly he would have been bit.

These type of situations have been hapening for about the last 3 months. We have noticed he does not get as excited as he use to and is sleeping alot more and when friends are over he seems to go upstairs where a few months ago he would be the center of attention.

Health wise he eats well and his stools are solid.  He does have a lot more gas and licks his chops which per the vet is common in older Boxers.  Sometines when this happens he throws up.  During the last 3 months we have had the biting problem he has only thrown up a couple of times.  

Help!!! What do we do?

Answer
Something is physically wrong or neurologically wrong.

If your vet cannot find this cause, I suggest you seek a new vet; one that is Boxer-savvy.

Boxers (any breed of dog) just doesn't start biting like that after being raised as a puppy, etc.

There could be arthritis pain causing him to react to protect himself when touched, or kidney malfunctions causing him vomiting and pain, or neuro problems causing nerve pain, etc.

Please seek a vet that will resolve the issue to treat him.