Fainting spell

So I'm just entering the 2nd trimester and I had a bizarre new symptom today. I nearly passed out in the shower! Like seriously.. everything was starting to go black. I had to sit down, but I needed to finish rinsing my hair so I could get out. I hurried to finish that and nearly fainted on the bathroom floor. As soon as I could stand up again I ran to my bed and laid down dripping wet. Feeling much better now, but this was really scary for me! Especially because I live alone at the moment! Any advice on what caused this or how to prevent it from happening again?