A decrease in menstruation after one day is an abnormal condition. It can be due to endocrine disorders that lead to irregular periods, or it can be a pregnancy-related disorder. Problems in any part of the hypothalamic-pituitary-ovarian axis can cause irregular menstruation. A sudden decrease in menstrual flow for one day may also not be a normal menstrual flow, but an abnormal uterine bleeding, such as can occur with preterm miscarriage and ectopic pregnancy. If you have a sudden decrease in menstrual flow, you need to go to the hospital for relevant tests, such as blood tests for HCG to rule out pregnancy, gynecological ultrasound to understand the condition of the uterus and adnexa and the thickness of the endometrium, and if necessary, blood tests for hormone 6 to understand the basic secretion function of the ovaries. After ruling out organic lesions, an occasional decrease in menstrual flow may also be related to endocrine disorders, which may be caused by excessive stress at school and work, as well as staying up late. It is better to change your habits, adjust your mind and relax to improve the above mentioned symptoms.