Perimenopause, the transitional phase before menopause, begins when the body starts to run out of eggs, causing hormone production to sputter as it adjusts to the new reality. As the egg supply dwindles, the need for reproductive hormones like estrogen and progesterone decreases, leading to unpredictable fluctuations in their levels.  Symptoms like irregular periods and mood swings (and literally dozens of other manifestations of hormonal changes) might occur as the body transitions toward menopause. It can all feel a bit chaotic.