I have often slept while riding horseback.

我经常骑马睡觉。

A whip means you're riding horseback; black gauze means you're having a dream; a couple of yellow silk flags mean you're in a chariot.

“鞭子”就是在骑马 “黑纱”就是在做梦 “几面黄色的丝绸旗子”则表示在马车上。