Maybe your locking your knees when u stand. I've never heard of eating more salt.
Oh but in pregnancy it's always better to have low blood pressure then high.
I had that with my 1st pregnancy. It's really nothing to worry abt. Just when u feel dizzy eat some sugary so u feel better. N try to eat healthy. Now when I delivered. My low pressure was so low that they had to keep me up. My husband would slap me lol. The doc said if it was any lower they would not b able to give me an epidural.