I have the same thing once in a while, sort of like when my eye will twitch, except it is in my lower abdomen. Are you pretty tired when this happens or just have finished exercising. I have some sort of pretty heavy duty exercise every day, whether it is softball, running, or rock climbing. Some days my body is completely exhausted. I don't know what to correlate it with either, but it doesn't hurt at all, and since I liken it to an eye twitch, it doesn't bother me.