Hi Dande,
Sorry to hear about your heart rate problems. Any time your heart rate slowly or gradually returns to normal, it is not a reentrant tachycardia like AVNRT, AVT, WPW, or VT. This tends to occur from inappropriate sinus tachycardia (which means that you get tachycardic without an appearant physiologic reason and we aren't sure why) or because of anxiety attacks. The key is always to catch it on a monitor to document the initiation and termination.
Inappropriate sinus tachycardia can occur in people with "dysautonomia." Again, this is not a well understood phenomenon. It absolutely could be a factor, but it is difficult to treat.
I do no know of a described relationship with cycles.
We tend to see more women with this problem.
The long term prognosis is no different than a matched population.
I hope this helps answer your questions. Good luck.