There are three solutions I have for you. If none of these work (Which I would be very surprised if they don’t) but I would try them in the order I put. I have tried these in different orders and they don’t work as well… Hopefully you will only have to use one of them…. Goodluck!!
I have eight horses, two of which I have right where I live and the other six are just down the road. I always have one horse right next to me. She(Snowflake) does what you are explaining all the time! She is spooked alot. UNLESS… she gets lots and lots of attention just to her. The other thing that will always always works is putting another horse with her. If this doesn’t work….. #2….
If your horse didn’t go from wide open space to closed off space then skip this…. We have three places that we keep our horses. ONE: Right where I live. TWO: Down the road. THREE: On our ranch. Our ranch is about 100 miles from where I live. We keep a horse or two out there for a few years. They get to know the place really well. Then when we bring them here to home, they FREAK. They will bite and kick and run all day. The reason is, out on our ranch they have as much room as they need. When you close them to a little area horses are like people… Sometimes. If you go from everything… to nothing… its not the greatest thing. So put a halter on them one or two at a time depending on how wild and crazy they are and just run and play with them. But at the same time make sure they are following every rule you taught them or else they will disobey all the time. Run and play with them for half an hour… if this didn’t work…. #3
The last recommendation I have for you is that if neither of the first two work… then try this. For this you are going to have to get a bit of guts for it. Saddle your horse up, make sure its tight and snug. Get a pair of stirrups on. If you don’t have these use a whip. (Stirrups work better) Take your horse and make him *walk*, not prance or trot, *walk*. If and when he starts acting up drive those stirrups right into their flanks. They are going to jump a little(you want this) once they do take one or both hands and turn them in a circle one way for six or seven times then the other way around six or seven times. once done that stop them say WHOA(or whatever command they have been trained by) in a loud, low but firm voice. walk them around for a while. Take him/her back to the same spot they got spooked before. If he doesn’t do it again, GOOD!! But he might have not noticed anything, so… keep doing this. do this everywhere until he is completely calm of his environment. If NONE of these work… I have a few more suggestions. But good luck on that horse!!