Hi Tulip,
I also think it is essential. There have been times when I felt really, scary bad, and my BP machine was able to tell me that my BP was jumping up and down hugely as was my pulse. When this was happening and once I saw from the machine, what was going, on I took a big dose of magnesium, potassium etc. and then my BP stabilized.
I used to be a patient of a dysautonomia specialist. He advised me to get the kind that has a cuff on the upper arm, has a digital read-out and memory, but does not pump up automatically. Since our BP is often too low, the automatic kind can pump up way too tight for comfort (and make you feel worse!). He said to get one with a bulb pump which you can do with the other hand. Then you can pump it up as much as you want.
In the US, they have drugstore brands that are very reasonably priced and even give you an in-store rebate, so though mine is a good one, it only cost about $20 with the rebates. (CVS brand). I know you are in Aust. and this won't be the same, so this is info for those in the US. But, a good one is worth it. I used to just take my machine to the doc and he could scroll through its memory and see the pattern of my BP by date and time.
Sushi