If you think your horse has colic, the first thing to do is call the veterinarian. While you wait, take your horse's temperature, pulse and respiration. Walk your horse but do not let him graze. If the horse seems quiet, he can be returned to his stall. He can lie down, but keep him from rolling.
Do not administer any medication before talking with your veterinarian. Remove all feed, hay and edible bedding such as straw from his stall. Allow him free access to water. Check to see how much manure there is in the stall. Look over the stall for signs of rolling or pawing which may have occurred over night or in the past couple hours. If the horse attempts to roll, get him up and walk him if you can do so safely.
For more information, please read Colic In-Depth.