It appears that Dave's book includes cancer and viral infections among the differential for his condition. From his description, these are reasonable concerns. Other possibilities include anything that can make lymph nodes swell, such as cat scratch fever, sarcoidosis, TB, AIDS, and local bacterial infections. There are lymph nodes along the sides of the neck. Swelling in this area is often from inflammation or infiltration of these nodes.
Inflammation comes from infection or irritation, infiltration from cancer cells.
Inflamed nodes are typically tender, warm, and firm but not hard. Hard, painless swollen nodes are more concerning for cancer. Both cancer and infections can cause fevers, fatigue, and other symptoms. You need to see a doctor, have a good examination, and probably some tests. The general process probably occurs this way for most clinicians.