Why would one lymph node in the neck be swollen and not the other? what causes them to swell?

. General swelling of lymph nodes throughout your body — which may indicate an infection, such as HIV or mononucleosis, or an immune disorder

Swollen lymph nodes usually occur as a result of exposure to bacteria or viruses

we have more emotional issue than ever in this country. with those emotional issues comes a lot of mental illness whether it be depression, bipolar disease, ptsd etc. having emotional issues comes with a lot of guilt and pain and people tend to stuff their feelings with food, drugs alcohol. however food is the most common and obesity is growing in this country as fast as mental illness is.