She's had bad impaction colics twice since I've had her, and both times we were lucky - at least part of the impaction was within reach of the vet's hand and the dosings with mineral oil and water did the trick. On the first occasion, when I had her boarded, she had to spend several days at the vet clinic and have multiple doses of oil. On the second occasion, the vet came to our barn and dosed her here, and she recovered more quickly. We use heated buckets and tanks at our barn, so the horses tend to drink (the boarding barn I was at when she coliced the first time did not have heated buckets and Maisie prefers warm water). As a precaution, I also add plain (uniodized) table salt to her feed to encourage drinking. I don't use electrolytes as they can increase urination.
I took her out of the stall and took a closer look. Her head was down and she was quiet, although she was still able to interact with us. She had high and low gut sounds on both sides, which was good. We walked very briskly up and down the barn aisle for a while - Maisie almost had to trot. I didn't give her any Banamine because I wanted to see if it would resolve on its own, and Banamine can reduce gut function, which can be a bad idea with an impaction. I would have also called my vet before giving her any. After a while, she started to let out some gas - lots and lots of gas. I put her back in the stall to see what she'd do. She passed more manure - not quite as hard. I put a chair in front of her stall and put the stall guard up and sat there for a while with her. She still wasn't interested in a treat or a handful of grain. More gas passed through. Bob the barn cat was sitting on my lap and she was enjoying "snuff-a-whuffing" him - she loves cats and I'm always amazed how gentle she is with them - she sniffs them and gently ruffles their fur. After about 15 more minutes she was clearly hungry. I didn't give her her PM feeding, but left her some hay to eat.
Before I went to bed, I went to check on her. She was resting quietly, had eaten her hay and there was more manure. This morning, she was completely normal. There was lots of manure - a normal amount - I pay a lot of attention to this with her because any reduction in the amount of manure can mean that there's an impaction brewing even if she's not yet in any pain. The manure was still dryer than I'd like, so we'll be keeping a close eye on her. I think this was just a gas attack due to the new round bales we got several days ago.