Severe Dysmenorrhea with Dehydration or Vasovagal Response: The patient's severe menstrual pain and altered mental status could be attributed to severe dysmenorrhea, which is a common condition in women of reproductive age. Dehydration or a vasovagal response to pain could exacerbate symptoms, leading to altered mental status.

Ovarian Torsion: Although less common, ovarian torsion is a possible cause of severe pelvic pain and could lead to altered mental status due to pain and potential decreased blood flow to the ovary.
Ectopic Pregnancy: Given the patient's age and symptoms, ectopic pregnancy should be considered, especially if there's a possibility of pregnancy. Altered mental status could be due to internal bleeding or severe pain.
Pelvic Inflammatory Disease (PID): PID could cause severe pelvic pain and altered mental status, especially if the infection is severe or has spread to other areas.

Ruptured Ectopic Pregnancy: This is a life-threatening condition that requires immediate attention. Altered mental status could be a sign of severe internal bleeding.
Ovarian Cyst Rupture: Similar to ovarian torsion, a ruptured ovarian cyst can cause severe pain and potentially life-threatening bleeding.
Septic Shock: Although the patient's vital signs are relatively stable, septic shock from any source (e.g., PID, ruptured appendix) could present with altered mental status and should not be missed.

Adrenal Insufficiency: Although rare, adrenal insufficiency could present with altered mental status and abdominal pain, especially if the patient has a history of adrenal disease.
Porphyria: This group of disorders can cause severe abdominal pain, neurological symptoms, and altered mental status, especially during menstrual periods in some types of porphyria.
Mittelschmerz: While typically not severe enough to cause altered mental status, mittelschmerz (ovulatory pain) could be considered in the differential, especially if the patient's symptoms are related to ovulation rather than menstruation.