Endometriosis can cause “endo belly” due to inflammation, hormonal fluctuations, and irritation from endometrial-like tissue growing outside the uterus, which leads to fluid retention and digestive disruption. This can make the abdomen suddenly swell, feel tight, hard, and painful, especially during flare-ups or around the menstrual cycle. Unlike normal bloating, endometriosis-related swelling is often more severe, longer-lasting, cyclical, and associated with pelvic pain, painful periods, or digestive issues. You should consult a doctor if the bloating is persistent, worsening, or interfering with daily life, as proper evaluation and management can help reduce symptoms and prevent complications.