Yesterday we noticed that our dog was acting strangely. He seemed tired and didn't beg for dinner like he usually does after we eat. Instead he just lay on his bed. He did eat his dinner, though. This morning we noticed that he had a large lump, or swelling, on the back of his neck. His neck is stiff. Pressing on the lump causes him pain. Please note: I've researched it on the Internet for a while. It is NOT lymphosarcoma or anything of the sort, as it is in the middle of the back of his neck, not near the lymph nodes. Please help!