Pain in small area in mid neck, just under chin, left side only. how to tell if i just slept funny and hurt muscle, or if lymph nodes or vein problem?

Sleeping funny: It's possible that "sleeping funny" might cause a muscle pain. Pain from a vein is unlikely but a swollen lymph node is quite possible. Is there a lumpy feel to that part of your neck that is not the same on the other side? Did the pain continue beyond the next day? A swollen lymph node may be from an infection in your mouth, perhaps a cavity in a tooth, or perhaps a skin infection (acne).

ENT consult: There are many vital structures in the neck region. Trauma related injuries are usually limited in size and duration of one week or less. If the pain increases in size, duration, and intensity, it is best to have an ENT consultation. If it is limited and goes away, it is likely trauma related. Seek consultation for recurring pain/problems.