I have an almost 8-year old Thoroughbred gelding, Spirit, who has twice in the last week had what seems like the horse-equivalent of a panic attack. The first time was during a lightening storm, when he woke me at 12:30AM to constant loud whinnying/screaming. I ran out to the run-in stall where was trotting in circles and highly anxious. He is very bonded with my other horse, who is miniature stallion named Quickie. Quickie was not in the stall with him (they both move freely about a 1.5 acre pasture). When I went out there, Quickie came into the stall and Spirit calmed down. I wrote it off as a spoof, thinking it was just a phobia of the lightening combined with feeling alone.
This happened again this evening, where Spirit acted the same way (trotting in circles, head tossing, inconsolable by me). He in fact jumped out of the stall, hurting his pasterns in the process, and repeated this several times before I could stop him. Needless to say, his behavior was highly erratic. He eventually calmed, as I went and got the other horse and fed them both (this was at feeding time, but he has never acted remotely like this at feeding time).
Any thoughts on what could be causing the sudden change? They have gone from round bale 24hrs back to squares, so hay is moderately less available (although I feed 1/4-1/2 a bale at each feeding and they are in a pasture with some scruffy grass). The other change is the weather--we are in Ohio, where it is incredibly wet, very muddy, and the temperature changes day by day (we are shifting from 40 to 70 in just a day or two).
Thanks for any input!