I fantasized about writing music.

我曾幻想作曲。

He sometimes fantasized about winning the gold medal.

他有时幻想赢得金牌的情景。

As I lay there a while, I drifted into a dream-like state and fantasized about what she looked like.

我躺了一会儿，进入了一种做梦一般的状态，幻想着她的样子。

Have you ever fantasized about...

你从没幻想过。

Also fantasized and she lives a baby.

还幻想和她生个宝宝。