Very rarely I develop a crush. This is the emotional rollercoaster I go in in the process.

Amazed- They amaze me. They are attractive, funny, brilliant and great to be around.

Embarrassed- I get all blushy. I am suddenly conscious of how dorky I am.

Happy- I like them. I am happy to have such a person in my life. The world is good.

Doubt- I doubt myself. I am not good enough for them. They'd never like me back.

Depressed- They'd never like me back.. I am so lame. Gah. I hate this.

Hmph- Pretty much giving up. They won't like me back, why bother?

If they like me back, they tend to ask me out in my 'hmph' stage.
That or I gather up my courage to confront them.