Diarrhea for 36 hours. don't feel sick; a little bit tired, otherwise ok. no fever or chills. should it stop by itself or is it serious? antibiotics?

Self-limited: Most cases of acute diarrhea are self-limited, caused by infectious agents (e.g. viruses or bacteria), and do not require medication unless the patient is immunocompromised. Most important thing is adequate oral intake that can be achieved with soft drinks, fruit juice, broth, soup, and salted crackers. If persisted for more than few days, see MD.