IBS and occasional extreme abdominal pain late at night

Hello,
About 2-3 times a year, I am awakened by extreme lower abdominal pain, that must take its course of about 45 minutes.  There is some urge to defecate, slight nausea, and "going" seems to relieve the pain only a little.  When I have these attacks, I can sometimes feel and hear what sounds like movement in my intestines, a sort of transit sound, like liquid, or hard matter are being pushed / forced? through a section of my insides.  

I have had these attacks for many years, and the pain makes me feel a bit nauseous (I never ever throw-up), and the pain is so intense that I have come close to passing out.  4 years ago I had a full colonoscopy, and it came back normal.  No obstructions, etc., at least during that test.  

The pain has me so panicked sometimes, that I almost call paramedics, but usually after about 30-45 minutes, it subsides, and then I go a while again without an attack.

Passing gas, or feces, only serves to give a little relief and the process is scary painful..

Any ideas?