I did something a bit silly: I had overloaded my neck for few seconds a couple of times while holding my 2 years old son with it, who weights about 15 kilos. Basically we were playing, I had my head inside his tshirt and I was holding him like that, without my arms... just with my neck, this made him laugh a lot...
But then I suddenly had pain in my neck.
Now my neck hurts, but not continuously: it happens only when I do certain movements, either if I am moving my head from bottom to top (say looking at floor and then looking at the ceiling, but then again not always) or when I am walking and I put abruptly my weight on my feet. I hope you see what I mean.
What can this be? Can an orthopedic doctor tell me what has happened?

The pain is not constant. It's only when I do certain movements (and not always) that I described above. It's not unbearable but it's worrying and it's somewhere between nerve and mechanic.. beside I am not quite sure how to describe it.
I am a male, 39 years old. Should I wear a neck collar for a while or something? Should I go to the A&E? Should I try to move as least as possible? I was thinking of going to a physioterapist close by tomorrow and ask but I am not sure if I should see a proper orthopedist first.
Thank you in advance for your advise.