Im not sure if drinking water would be much to do with blood pressure, but if you get dehydrated it can probably cause you to feel lightheaded and dizzy, so its just a good idea to drink alot more anyway, i find water tastes strange sometimes,so i add a bit of squash. If you feel funny just try to take a break from what you are doing for a few mins, our bodies are are doing alot of work right now, i always say to my OH when he wonders why i'm so tired- i'm growing a little person in my stomach so of course im going to be tired!lol I found 2nd tri is alot easier though, most symptoms ease up alot and you feel a bit more human lol. Although this time round i have a toddler so not sure if i'll ever have much energy again!