IBS or Irritable Bowel Syndrome is a very common affliction. It is estimated that 20-30 percent of the population in the USA is suffering from it.
Actually, IBS is a broad name for many kinds of symptoms and unpleasant sensations of the guts: bloating, cramps, pains, nausea, constipation or diarrhea (sometimes both together) and many more. A typical feature of IBS is that the symptoms mostly unfelt during sleep. Another interesting feature is those symptoms are mostly coming in addition with psychological sensations, mainly anxiety and depression which is why it's sometimes called 'sensitive bowel syndrome’.
The main causes of the syndrome still are unknown, but the assumption is that it is connected to the gut peristaltica, gut muscles cramps and movements, that become irregular - sometime too fast, too slow or both. Some scholars explain the syndrome as oversensitivity to sensation at the guts. In one study , a special balloon was inserted in the guts of IBS diagnosed and other healthy volunteers. This balloon was blown up to different levels to make pressure on the side walls of the guts. Then the researchers compare the reaction to pain a sensation between those with IBS and the others. As expected, the IBS group reacted worse to the same amount of pressure.
Other theories relate IBS to a problem at our serotonin receptor at the guts  that are similar to those in our brain. The digestive system is known as our second brain, the brain that is connected to the emotions. It is where we are “digesting” our feelings. Those two brains have a large effect on each other. Serotonin is one of the main hormones that related to our moods and feelings. It may be a chemical explanation of how feelings affect our guts. IBS is a fascinating example of it. There are many other theories about IBS cause. For example parasite infection as a trigger, food intolerance and many more…