Dehydration/seizure

I'm 12 weeks 3 days pregnant and yesterday I was making the kids lunch and I started to feel dizzy and sweaty and the color drained out of my face. I know what it's like to faint so I started to head towards the table so I could sit down. Just before I reached the table I started to gray out, I drop to my knees, I couldn't see anything and then I started to convulse. I was aware of what was happening but there was nothing I could do. I couldn't control my movement and I couldn't see anything. I called the OB on call and he said to come in immediately to the ER, so I did. They determined that my blood pressure was out of whack and that I was severely dehydrated which cause me to faint and seize, which was surprising to me considering I drink fluids all day, I eat fruit and other things that are watery in substance like broth etc. The doctor asked me how much fluid I take in a day and I told him I drink at least 8 glasses of water among other things, he told me during pregnancy I need to double that! I dont know how I can double it when the amount of fluid I intake is already pretty much my max. He said Gatorade is good too so I picked some of that up. This is my third pregnancy and I have never been dehydrated before, I've also never had morning sickness (mostly just nausea, very little vomiting) like I have with this one so maybe that has something to do with it 🤷 Anyway I'm supposed to be on bed rest until my OB clears me but with 4 kids I'm finding that impossible. My SO's kids leave to their moms later today so that should help but I'm really scared. I don't ever want that to happen again, it was awful. Has this happened to any of y'all and do you have any tips to prevent it in the future?