New anxiety. Old anxiety, louder. The 4 a.m. dread.

Why this is happening now

Your brain's calming systems run on hormones that are now swinging hard or dropping. The wonder isn't that mood shifts, it's how often nobody tells women to expect it.

1. 01

   Your calming chemistry is running on a hormone that's now swinging hard

   Estrogen doesn't just decline in perimenopause, it lurches. And it happens to be tangled up with serotonin, dopamine and GABA, the systems that regulate mood, motivation and how quickly your nervous system settles. A steady fall is one thing. The swings are what push reactivity up and the anxiety threshold down.
2. 02

   You're also losing one of your body's built-in chill switches

   Progesterone gets metabolized into a compound (allopregnanolone) that acts on the same brain receptors most anti-anxiety medications target. As progesterone drops through perimenopause, that quiet built-in calm goes with it.
3. 03

   Your stress response has a shorter fuse than it used to

   The same email that used to roll off you now lights up your stress system for hours. That's the HPA axis (the body's stress-hormone loop) becoming more reactive in perimenopause. A rough night's sleep amplifies all of it, which is why bad-sleep days feel bad-mood days.
4. 04

   The rage isn't a personality change, it's a mood symptom

   Anger and irritability are mood symptoms too, they're just less socially acceptable than sadness so they get less airtime and less sympathy. Sudden, disproportionate fury, especially in the week before your period in late perimenopause, is a well-recognized pattern, not a character flaw.

5. 05

   Bad-PMS weeks can turn up in your 40s, even if you never had them before

   Some women who sailed through PMS their whole lives suddenly get walloped by it in perimenopause. Others who had it badly as teenagers see it come back. Clinically this pattern is called premenstrual dysphoric disorder (PMDD), and the good news is the worst of it usually eases once periods stop.