weird behavior has me worried

So last night I went into the garage to check on and visit our 5 week old silkies, I noticed one of them on its back kicking its legs, I uprighted the chick and immediately it put its head between its legs and did a somersault and went crazy rubbing its beak a crossed its breast, I watched the bird for about 5 minutes doing this over and over, I decided to quarantine the bird to make sure it wasn't sick, as I held the chick it did somersaults in my hands, its been about 20 hours now and its still the same story, it eats and drinks just fine and I watched it take a nap too, the stool looks normal and I'm really hoping for some feedback to help me understand whats going on, please and thank you.

 

Wry neck sounds exactly right, thank you for the help, so grateful for this website, just wish in all the research I did before letting my gf buy silkies it would of mentioned the hole in the head they have that doesn't protect their brain, just wondering if they are gonna be safe around my 2 barred rocks and 9 new hampshires, they are really tame birds but I almost don't think it will be worth the risk in letting them share the same coop.