I Am Pregnant And I Recently Got Into The Shower

I am pregnant and I recently got into the shower with the temperature I usually have it at . More to the hotter side. And I started to feel dizzy and end up falling and couldn't get back up because my legs had given out and I tried multiple times to get back up and I finally was able to and stumble out of the shower into my bedroom to lie on the bed. I was fine after a minute or so of just relaxing and breathing. Why did that happen?