Ah yes... the most easily understood language a horse will speak to you: That of joy and exuberance. I have some mutts, some grade quarter horses, a registered QH, a BLM yearling, a grade paint filly, and a registered paint mare... they all do this.
Spring is coming, they know it, they feel it in their bones, and with it, comes this display of joy.
I've even ridden our Old Man... a 25 year old last summer... on trails... and he will leave out with a spring in his step, a light in his eye, and his tail hitched up almost the entire time. If it was a pain response, he'd launch me out of the saddle - he won't tolerate block headed people. Neither would he take off at a trot or a short lope. He'd plant his feet and refuse to move.
I especially like seeing that tail up, hearing that snort... and watching one do the boing-boing run across the pasture. They will bounce like a bunny hop sometimes, that tail just a flagging.
It's joy... allow yourself to be caught up in it!
"We are here to laugh at the odds and live our lives so well that death will tremble to take us."