Is it normal to suddenly develop feelings for a platonic friend?

So... I recently (~ a month ago) asked this girl who I liked out, and she said no. She was nice about it, but essentially what was to be gotten from it was that I was friend-zoned. So, for a couple days I bitched about it to a bunch of people, all of whom were very unhelpful. All except a platonic (female) friend who I've had for years. She was unspeakably helpful about it, and after about a week, I was more or less over it, and moved on with my life.

So, anyway I have never had a problem with our friendship before, but last night I had a dream about her. It was, I suppose you could say, sexual in nature, but that wasn't the real point of the dream. It was more of a "relationship dream" than a sex dream. But I'm not sure why I had it about her. I can't tell if it's simply my loneliness manifesting itself, and she was the one who most recently impacted me the greatest, or if it's some suppressed feelings for her. I don't really have feelings towards her, but I've been thinking recently, and I feel like if she were single, I wouldn't mind dating her.

So... I guess my question is, first, is it normal to have this type of feeling? And secondly, which does it seem like the origin of this is? Just my loneliness, or some suppressed feelings for her?