I'm very sorry for you and your horse. Hoping he is better soon.
Becky
It looks as though we've passed through the worst of it. He is no longer worried about his discomfort and in extremely interested in the two mares twenty feet away.
We are going to watch him for a couple more hours before we put him back in his stall and then feed bran mash tomorrow morning.
Can't find a cause for it other than maybe our really lousy weather - his feed and hay is all fine. He has a heater in his water so he should be drinking enough.
Anyway, thank you everyone so much. You guys are the best :)