I can relate. I have anxiety as well as hypertension. Heck, was officially diagnosed with hypertension at the age of 17. And because it's hereditary they believe that is why I have it.
(Of course I'd still like to know the physiological or chemical cause - you know, the actual mechanism at work that causes my relatives and myself to have hypertension, but I currently don't have an answer to that that question.)
But in any case, my anxiety tortures and debilitates me but it's especially torturous and consuming when it comes to my blood pressure.
So hopefully I can help to answer some of your questions from my years of experience with this topic.
"1. Simply, how long should it take for the meds to lower my BP? When should I start to see a noticeable reduction?"
For me and what I've read, it takes an hour from the first dose for it to go into effect and supposedly it's at peak effectiveness after 6 hours of having taken it... although in my experience that time-frame can be more around 8-10 hours.
"For me, however, I am wondering whether there is an association between high blood pressure and increased nervous system activity."
I have been informed that this is definitely possible, with the exception of the fact that each person's hypertension differs in cause from person to person. Your sympathetic nervous system, if it was overactive, could result in hypertension.
But keep in mind that the hardcore, bottom-line data to support this current view is lacking. Hence why I say it is "possible".
I also believe it is possible that your anxiety is raising your pulse as well as your blood pressure. The fact that you're feeling "tense, nervous, anxious, unable to concentrate and very fidgety" as well as your "difficulty sleeping" and your loss of "loads of weight" because you're "not eating that well" tells me that you most likely suffer from anxiety either before being diagnosed with hypertension or as a result of it.
Now, I would love to tell you that science currently has an answer as to why anybody/everybody has hypertension and that they have a solution to resolve it... but unfortunately they either don't or they're holding back lol.
So in the meantime, we must take our own steps to keep our blood pressure at a healthy average (as well as take our medications for as long as we need them).
Start with lowering your anxiety by means of counseling of one form or another, or in other words... talk it out. Talk about the times you feel anxious; the thoughts running through your head before, during and after; the emotions you're going through; etc.
Try to find the main causes of your anxiety by keeping a journal (don't forget to include the foods you eat as certain ones can cause anxiety, or what you were generally doing before the anxiety came), and then work towards retraining your thought processes to become less anxious and less worrisome.
The next thing I'd suggest is (depending on your medications) try including a healthy amount of bananas (or potassium) and peppers (or capsaicin) into your diet as they both have a lowering effect on blood pressure.
And lastly I'd suggest exercise, specifically in the form of cardio as cardio has a GREAT blood pressure lowering effect.
Hopefully I have helped in some form or another.
If I have failed to answer anything or you have more questions feel free to ask!