Usually, a painful experience is the result of resistance and tension.  A professional colon therapist is skilled a putting you at your ease and minimizing discomfort.  Most people actually enjoy the colonic and are pleased with the unaccustomed sensation of feeling lighter, clean and clear afterwards.  Sometimes during a colonic, the colon muscles will contract suddenly expelling considerable amounts of liquid and waste into the rectum.  This may feel like cramping or gas and may create a feeling of urgency to empty the rectum.  Such episodes if they do occur are brief and easily tolerated.