Because I have anxiety problems and my body dosen't handle stress very well. Over the past 20 years my body has handled stress in different ways, for example: I went thru a period where I would get zits really bad when I was stressed out, then after a few years of that, it seemed like the stress transferred itself to a different part of my body and I had 3 ulcers, then after the ulcers, I got real bad headaches, then after the headaches, the IBS-D came on. I would trade the IBS-D for the zits again if they'd let me.Lena