Hey, I just posted a long reply on your other thread for this little one.
The video is the chick looking for her mum and clutch mates, and the warmth and comfort that offers (as well as the obvious, food).
The laying flat, I´m not 100% but it could be ¨giving up on trying to move¨. I wrote on your other thread about bedding, and not using paper towels and paper. There´s no grip, and for a little creature like this, they need the grip to be able to move, or they are walking and not getting anywhere, like running on ice but staying in the same spot. Get the brooder lined with the shavings, and create a small dip for the chick. They like to snuggle or touch other things (clutchmates/mum/dad etc), Do you have something so small made of cotton fabric? Maybe a hair scrunchie you can tie in a small ball? To put in the brooder with the bird? You can´t use something too large or it may fall on the bird and smother them.