Should I go to the emergency room?

Okay first off. I'm a younger mom. But this is my second pregnancy. My first one was easy no problems no complications at all except heart burn. 
I'm 26 weeks and was just shopping with my mom . We were in check out and all of a sudden I got cold then really hot and dizzy and light headed. As it got worse I thought I was gonna faint so I walked to the bathroom and sat down and it went away after a couple minutes. What could this be ? She said I'm just exaggerating. But this pregnancy I've had a lot of weird she happen and I'm honestly scared