What Causes Severe Constipation And Bloating When Diagnosed With IBS?

Hi. I have been diagnosed with IBS because of my problems with severe constipation and bloating. Now I have started having these attacks where, all of a sudden, without any warning, I get so dizzy that I feel like I am going to black out . I immediately put my head down to prevent that. My stomach just aches and hurts so much. Even after the dizziness lessens, I am totally wiped out and have to sit for quite a while before I dare get up. The dizziness lasts anywhere from 5min. to a half hour. After I am able to get, I usually have a bowel movement. Ordinarily, I only have a bowel movement about 1 - 2 times a week but I can t seem to go much even then. I have stopped driving because I don t want this to happen while I am driving. What could be causing this?