The automatic movements of the digestive system are largely controlled by you nervous system. In a stressful situation, your nerves are negatively affected, so that our digestive system, for example, can become overactive. In a stressful situation, your nerves are negatively affected, so that our digestive system can become overactive, for example. In other words, if you have IBS, your bowel movements may be overly responsive to even the slightest disturbances in your digestive system.