Well, I don't want to set myself up as an authority. I haven't experienced peri from the "inside", and I'm no doctor.
But in a nutshell, perimenopause, or pre-menopause is a transitional stage of two to ten years before complete cessation of the menstrual period. Its average duration is six years, and can appear in women from 35 to 50 years of age. The symptoms are basically the same as PMS, with perhaps a few more thrown in, and they’re more constant. Or perhaps it’s more accurate to say that the physical and mood fluctuations are more constant and pronounced. A woman who’s had a tough time with PMS will likely have a rougher perimenopause than one who has had it relatively easy PMS-wise.
Like I said, I’m no expert, but I think I’ve been living through it (from the H perspective) for quite some time now, and I have done some research, so I will point anyone who's interested to some very good resources.
I think that one of the most important things to remember is that perimenopause/menopause is not a disease. I was loath to use the term “symptom”, but I can’t think of a better term. Perimenopause/menopause are a natural part of a woman’s development, and as such, are great opportunities for personal growth. Both for the woman, and for her SO.
But MAN! It’s hard! For both parties!
And I think it’s nature’s cruelest joke on humankind that this stage of a woman’s development coincides with the period of time when a man is most likely to go through one of his own... MLC!