This thread is not meant to shock or anything. It's just a theoretical interest.
When my period is about to start, I get more nervous, less sure about myself, more pessimistic, more organized and less efficient (yes, both). I lose interest in a lot of things, I see teaching as a chore (while normally I look forward to almost every lesson)...
We all know the period has an influence on our mood. Is it consistent enough to speak of a character change? For all practical purposes, you can describe me as a dark ISTP for a few days in each month. I'm not sure about the T part.
Is it a streak of Shadow mixing up with your usual self?