My surgeon says this happens to everyone after a hysterectomy. I asked if that meant that having the bodies' signs that a period was coming was enough to cause everything and she said absolutely not, that PMS is very real but she has no explanation for it. Sure enough I haven't had pms or the like since my hysterectomy and since menopause it's even better. Until this last year of horribleness I was noticeably better without hormone changes all the time.