Hi jedigirl
I had various problems for about 3 years with vertigo (very severe) headaches and just generally feeling like I was going to pass out. After a year of intensive testing where the only thing that showed up (mri's of brain, neck, ent visits etc) was very low progesterone, I kept a diary! My symptoms were very regular and always hit at the two weeks before menstruation. My estrogen levels were always very good! Specialist prescribed progesterone and symptoms went away within a couple of months (I also had chronic anxiety!!). All went well for a couple of years til my estrogen nose-dived to 15 - consultant said you have less estrogen than a man! At that point I added in estrogen. Symptoms I had from low estrogen were different - palpitations, adrenaline rushes through my head, high blood pressure.
I had lots and lots of blood testing - for progesterone always around day 23 of my cycle (I was having a cycle then!) although later when everything became completely erratic it didn't seem to matter when tests done as I was on hrt and they were testing these levels. Even with continuous progesterone I have struggled to get these levels up to 'normal' ranges. I know many people don't think progesterone has any wide-ranging benefits but my specialist is insistent that it's all about getting the balance right between progesterone and estrogen - it makes sense to me!!
Hope this helps.