In your life, you'll have 400 periods. You'd think that after years of cramps, crankiness and Kotex, you'd know everything there is to know about that time of the month. But if you're like us, you still have questions — weird questions — about your period. And so we asked the OB-GYN experts to help us solve the most puzzling mysteries about ever-menstrual ol' Aunt Flo:

Why are my dreams so vivid during PMS?
Although no research concludes that we dream differently in the week before our periods, studies do show that our sleep is disrupted. "Women who have moderate to severe PMS have sleep problems," says Diana Taylor, RN, PhD, and author of Taking Back the Month. "They're waking up more frequently or earlier in the morning, so they may be waking up in the middle of their REM sleep cycle when they're most likely dreaming." Since you remember your dreams only if you wake up from them, waking up often means PMS sufferers may be able to recall their dreams in all their wacky detail.

Why is my blood brownish at the start and end of my period?
When your tampon looks liverish, it means that the blood is trickling from your uterus more slowly. Margery Gass, MD, professor of obstetrics and gynecology at the University of Cincinnati, in Ohio, explains that during this gradual flow, blood oxidizes and becomes darker. "It's just like when you have a bright red drop of blood on a piece of fabric," she says. "[When] the blood is exposed to oxygen, it turns brown."

What's up with those gross clots? Should I be worried?
Relax. In most cases, they're no cause for alarm. "Clots mean that the blood probably sat someplace, either in the uterus or the vagina, before it came out," says Gass. "It had the opportunity to coagulate and clot." Consult your doctor if you are passing large clots (bigger than a quarter) or experiencing extremely heavy flow (soaking through an overnight pad and tampon within an hour).