I passed intestinal lining in my bm this morning. no blood in bm. no mucous. diarrhea, stomach cramps, gone. is this a sign of a serious condition?

Unsure: It depends on if it is truly "intestinal lining", which is hard to say without a picture. Although we do slough off cells regularly in our intestines, very much like how we slough off dead skin cells, it's a little unusual to just see "sleeves" of your intestinal lining without blood or diarrhea or any pain. I would just keep an eye on it. If it keeps happening, get checked out. Hope this helps.