Colic is a broad name covering basically any type of internal discomfort your horse is being bothered with, whether it be mild or severe. There are two overall categories of colic, medical and surgical.
Medical colic is basically a "bellyache" of unknown etiology that can be treated with banamine, walking and possibly the administration of oil to help move an impaction along the bowels.
Surgical colic, on the other hand, consists of a twisted intestine or a blockage in the intestines.
Some of the symptoms of colic can be pawing the ground, turning to look at the belly, sweating, pacing, biting at the belly, and rolling. Most mild colics can be relieved by administering banamine and walking. Walking keeps the horse from rolling and making things worse by twisting the intestine; it also stimulates the intestines. If a horse can get gas and manure passing, the problem many times is resolved. Keep in mind that it takes about 20 minutes for banamine to take effect.
My question to my veterinarian recently was, if I find my horse in distress, when do I call him? Each vet may feel differently, but mine told me that if the colic seems mild, administer banamine and start walking the horse - most are usually better after half an hour to an hour. He said that if I feel comfortable doing this, then just call him to inform him about what’s going on and he’ll call and check back a little later to see if the colic has resolved.
But if the colic seems severe, or if I don’t have any banamine on hand, my vet told me that he wants to be called out immediately.
I know from experience that having a horse with colic is a scary time. Luckily my few times dealing with it have been with mild cases and only once have I had to actually have my vet come out to help me, and even then it was resolved fairly simply. May your experiences be the same!