Help??

27 weeks pregnant. I’ve been having a pounding headache for the last two days, it finally started to go away today. However when I was doing dishes, I started seeing black floaters, my face got so hot, my heating went and I knew I was about to pass out so I hurried up and laid on the couch. Blacked out for maybe a minute, if that. I called my doctors office and it being Saturday, it was an on call doctor. All he told me was I was dehydrated?? I just don’t know... I’ve been pretty much living off of fluids due to my severe morning sickness. I did try to drink some juice and lay down but I still feel so blahhh. Help??