It appears a previous answer didn't post, so I'll answer your question. Your reddish brown stool likely reflects some bleeding in your lower GI tract. It sounds like you have had some bowel difficulties in the past and were diagnosed with IBS (irritable bowel syndrome). Your bleeding likely either represents infection ( in which case you need to be seen now for treatment) or IBD (inflammatory bowel disease). It is possible that you were mis-diagnosed in the past with IBS and are now presenting with IBD.
Either way, you are likely bleeding from your GI tract and are not feeling well. You should be seen by a doctor NOW for evaluation.You should have someone else drive you, or call 911.
I strongly recommend a colonoscopy once you are more stable to look for IBD, which consists of either Chron's disease or Ulcerative colitis.
In the meantime, I wouldn't take anything by mouth except water.
Good luck and I wish you well.
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The reason I've told you to avoid eating foods is because I feel you should be evaluated by a doctor for what may be bleeding. Anytime a patient may have bleeding in their GI tract, it is best to keep an empty stomach/colon in the case that a doctor needs to take a scope and look to find the bleeding.
Unfortunately, it sounds like you haven't seen a doctor yet, so you obviously can't starve yourself. Please get to a doctor to evaluate your stool changes!