worried !

So I'm almost 19 weeks , last night as I got out of the shower I started to feel over heated and kinda dizzy . I drank some cool water and went and rested . Fast forward to today at 11 am I was in Walmart I get all dizzy and light headed my vision got very blurry. I felt so sick all at once and very cold . I called my husband he came and a manager helped me to sit down and we called my ob she sent me to ER . At 6 pm the doctor said he couldn't find anything wrong , and just to watch out it doesn't happen again. I have diabetes ( my sugar was normal) blood pressure normal and all labs normal. They did a sono and the baby is fine ! Thank god but I'm so confused .