Scared - Passed out

Today at church I felt like I couldn't breath, I was sweating real bad. I kept telling my husband I feel weird, I can't breath and finally said I'm going to pass out. By that time I was unaware of what was going on. I was speaking loud and had my shoes off trying to cool down. I blacked out and my husband pulled me out into the hall. I was probably within 10 seconds of passing out. I am trAumatized. I feel nervous stressed, scared, anxious. Why did this happen? What can I do to  prevent it? What should I have done? It was so scary. I'm 15 weeks a couple days. Planning on calling the dr tomorrow.