Is it normal to see a person's face everywhere

i have this friend I love spending time with. Most of the time I miss them. (we are girls btw just friends) today we were on a trip that I was dreading because I thought I'd have no-one to go with, she offered me to go with her coz she had no-one either. I was excited about this but then I met a different friend and went with her. But my other friend was with someone to so we were both not alone.
I had soo much fun with this other friend, that I forgot about my other friend. But then everywhere I looked I can see my other friend, everyone looked like her, I saw her everywhere. The strange thing is i could never visualise her face in my mind before and now it didn't stop. This has freaked me out, anyone know why this has happened?