You need to go to an emergency room.
The suggestion to check the blood pressure monitor was on the money.
You have a potentially life-threatening problem that must be dealt with immediately.
A September 9th appointment is unacceptable.
The first thing I would do is check to be sure your blood pressure monitor isn't malfunctioning by either purchasing a new one, or if you go to a clinic that has emergency care, ask for a simple bp check. Supermarket bp checkers aren't always accurate I'm told, but try that too. Your pharmacist probably would check it for you for no or little charge.
That said, it's possible that a long-term high blood pressure problem could have caused your heart to enlarge and thicken, perhaps the valves aren't closing completely, there are a number of reasons bp drops. What is your pulse doing? Do you experience symptoms like aggitation, light-headedness, weakness, etc?
Swelling of the ankles and feet could indicate that your heart isn't working right and you could be retaining water. Do you work on your feet? I would certainly suggest that you throw away your salt shaker, and as much as you possibly can, eliminate processed foods. If you smoke, stop, it's the worst possible thing you could do with your symptoms.
Do keep us informed once you go to emergency care or wait to see your doctor as to the cause of this problem.
I would not guess what is wrong, but there is no way I would wait until Sept. 7. I would go to ER now.
crow264