Horses may get colic for many reasons. It can be something in their diet, stress-related or often times something they ate that is just not supposed to be edible. Colicky horses are like colicky babies because they have a terrible stomach ache, but on a much larger scale, due to the fact that if they don't either pass the foreign item or pass a stool at all they may actually die. This can happen in the span of only a few hours and it is critical that you help them.
In treating a colicky horse you must remain calm. If you are upset it will further upset them and make the condition worse. If the horse is repeatedly laying down and then getting up again, then you probably have noticed the signs in time to help. Make the horse get up. They may be groaning and in pain, but for them to pass a stool they have to be standing up. Cool the horse with water from the garden hose and walk him anywhere that he can reach fresh green grass. Try to get him to eat the grass for fiber even if you have to hand feed them. If they refuse the grass, then walk the horse constantly until they pass a stool. This can take up to 24 hours of continuous walking. A good treatment that always helps a colicky horse is to give them cooking oil. Put at least 1 cup of cooking oil in a large syringe and squirt it down their throat. Also squirt 1 cup in their rear end as deep as you can get it. If no cooking oil is available, a water bath in their rear end will act as an enema and pass the substance.
At first signs of a colicky horse you want to immediately quit feeding him any sort of grain or food except for grass or hay. You will notice that the stomach of the horse will look very large and swollen. A cold wash cloth applied to the horse's face around the eyes and nose will help them to feel better and always pet and rub them to calm them.
If these treatments do not give your horse any comfort, it is time to call the vet. A farm call is your best bet so the horse doesn't stress even more with a trailer ride to the vet's office. The vet will come out and usually administer shots of pain killer and give the horse a stool softener and enema. As soon as the horse passes a stool, they should be fine, but you will need to watch him for a few days to make sure that he has passed all of the substance that made him a colicky horse.