My HormonologyNext time you’re planning to do something frightening (say, seeing a thriller or visiting a haunted house), try to avoid doing it during the first half of your Week 3, which is about 16 to 20 days after the onset of your period. According to a new study in the journal Neurobiology of Learning and Memory, the combination of plunging estrogen and rising progesterone creates brain changes that make stressful experiences more traumatizing, prompting a three-fold increase in unwanted “intrusive thoughts”—memories of the stressful event you just had or ones you encountered in the past.

Want to know the best time of your cycle to see a fright-film? Aim to do it in your Week 2. That’s when high estrogen and testosterone ratchet up your enjoyment of scary experiences by boosting your desire for surprises and spine-tingling thrills!