About to pass out? what's going on?

I'm pregnant but this has happened before so I don't think its related. I hadn't eaten and I was standing in line at the courthouse and suddenly my vision started blurring and to the point where I can hardly see, my hearing went almost completely away it felt like what it does when ur in high altitude but much worse. Was sweating like crazy, cold sweats too. Felt real dizzy and all symptoms passed once I was able to be seated.. Why did this happen? I have a dr appt later today but was wondering if I could get some insight before hand