I doubt it's low to be honest as I was borderline high before being pregnant and then got pre-eclampsia so went super high, never had low BP.
Ah, but it could be. And even 'low for you' blood pressure would have the same effect, because your body's used to it being higher than it is now.
Here comes the science bit:
The more sugar (carbs) you take in, the more sugar you need to store and the more your insulin levels rise. High levels of insulin can narrow the arterial walls which in turn, will raise blood pressure because a harder pumping action is required to get the blood through the narrower passageways.
But insulin also 'talks' to the kidneys. It tells them to hold on to salt. So the kidneys figure, okay, if we have to hold on to salt, we'd better hold on to water too so that the level of salt remains within safe limits.
Increased salt retention = increased water retention.
More water retention = more fluid = more fluid in your arteries and veins = high blood pressure.
If you reduce levels of insulin in the blood stream by reducing carbs, hey presto - you don't retain salt, so there's no need to retain water. The level of fluid in your arteries and veins reduces and your blood pressure goes down.
(This last bit, by the way, is one of the reasons why you regain several pounds very quickly if you fall off the low carb wagon because you immediately start making more insulin, which means you hold on to salt and water. The other reason is because you refill your glycogen stores in the liver and each gram of glycogen is bound to 4 grams of water. To put it another way, if you refill your glycogen stores with a pound of glycogen you'll gain five pounds
)
So if you've previously suffered from high blood pressure, doing a low carb diet is a very good idea. Many people (my CWPC is one of them) will be able to come off blood pressure medication if they do low carb - that's one of the reasons you need a doctor's supervision to do this diet if you take medication for high blood pressure.
But as I said before, if you are worried, it probably is a good idea to talk to your GP. Does the dizziness go away after a few seconds after moving or do you feel dizzy all the time?