Have you been able to get in to see a doctor yet? I am on lisinipril too. Last spring I had a period of very low blood pressure. My creatin had gone from 5.5 to 3.5. The improvement was because of damage to my kidneys after a misdiagnosis of an infection after a biopsy. When they attempted to drain the infection that wasn't there they had caused the damage that made it jump up to 5.5. It took almost a year for my kidney to heal. Which they had told me would never happen.
I don't want to get your hopes up or anything, but has there been any improvement in your function? I had read your other posts about the color of your urine. Please don't go by my experience. But maybe the medications you are on and diet changes you have made is making your pressure the way it is.
Be careful that it doesn't drop too low. I do know lisinpril takes a little while to get to a theraputic level.
As for your question about blood pressure dropping as function declines, I think it should be opposite. It should go up.
Like I said before please don't get your hopes up because of what I experienced. Stress can also cause a drop in blood pressure. I know that sounds crazy too. One of the first things I was asked was if I had any additional stress. Additional stress can triigger more hormone release that can cause it to drop.
How have your sugar levels been? That can also influence blood pressure.
Please keep us posted. I have been thinking about you.