Pregnant. Vision Gets Cloudy And Blackish, Ear Ringing, Heart Rate Elevated, Sweaty Palm And Hands. What To Do?

I m 28 weeks pregnant, I had an episode earlier today where my vision became very cloudy then blackish, my ears were ringing and all the background noise because faint. I ve been feeling bad all day before and after this episode. My heart rate seems elevated or almost uncomfortable, and its difficult for me to breathe, the palms of my hands are very sweaty. I have a doctor appointment tomorrow but I m getting a little nervous.