i have high blood pressure as well and have been wondering about the subject as well. I hope someone who knows a little more about the subject has some answers to this
Yes you can have a natural birth with high blood pressure so long as no other risk factors present themselves. You will be monitored closely but should still be able to do what you need to do for a natural delivery (if you have a midwife they'll most likely be with you for the entirety of labor and delivery whereas an OB will only be there when it's time to push).
The best thing is probably to get in the water and find something that is relaxing. That may seem like a weird thing to say but birth does not have to be as painful or traumatizing as women believe. When you get into a rhythm with contractions you will find yourself "zoning out" to focus. Just focus on relaxing things (waterfall, for example) and play relaxing music if it helps. Keep your breathing even (don't hold your breath) and remember that the pain is temporary. Fear causes the pain to be more painful because you tense up.