Horse galloped into this wood awning thing, completely stuck on hardcore… There goes an hour of gameplay.
It happened to me once in Skalitz.
Probable solution for you:
Take out the bow and shoot the horse in the neck.
tried fast travel out? works when I get stuck in a tight spot like a horse stall. Was suggested by another poster
He can’t because he’s in hardcore mode.
Just shoot the horse, is still my advice.
Try saving and loading the game. It helped me in all cases.
Shooting a horse is also a good idea. You’ll buy a new one 
Save & Quit, relaunch the game and Continue.
Has worked every time for me. No matter how stuck.