Can you get whiplash from someone playfully punching you in the arm?

I have never experienced whiplash (from car accidents), but the other day, I was punched (playfully) in the arm rather hard when I was not expecting it, and it felt like my neck stayed in the same place while the rest of my body shifted to the right. Yesterday I had a neckache (very dull pain, bearable), and today I can feel the same dull paid in the upper left side of my back as well as my neeck.

Whiplash is primarily due to sudden, rapid and intense acceleration/deceleration forces on the body, which is very unlikely to be caused by someone playfully punching you in the arm. Occasionally, whiplash is associated with sports injuries and is primarily due to motor vehicle crash events. If I had to give the general odds, I would have to say I would expect fewer than 99 our of 100 situations, where an arm was playfully punched, would be sufficient to cause a whiplash injury, barring significant pre-morbid conditions or complicating factors (fell down and hit the head or neck due to being punched, head was smacked against the wall due to the impact, et cetera). It would also depend on what you call "playfully punching someone in the arm", that is on the actually intensity, duration, peak forces, and potential repetitive nature of the punching. The only reliable way would be to have the person who was punched be evaluated and examined physically by a licensed and appropriately trained health care professional.

Yes! An unexpected punch might lead to a abnormal move of your cervical vertebrae and a muscular constriction. Try to take a pain-killer (e.g. ibuprofen), if the pain persist, consult your doc.