What do you mean by "I don't know why I thought of you last night"? How to understand this sentence?

What do you think of me? Let me see you in my dream.

From the Tang Dynasty poet Bai Juyi's Dream Yuan Jiu.

"Nine Dreams" Tang Bai Juyi

In the morning, the breeze is melancholy, and Tongchuan is without water.

I don't know why I dreamed of you last night.

The author wrote about the feeling of bleak morning breeze and the pain of friendship being cut off by Tongchuan and Qinshui. Yuan poetry is full of mountains and rivers, corresponding to white poetry, which aggravates the pain of friendship being cut off. I didn't say I was struggling to dream. I thought of Yuan Zhen and asked him why he remembered me, which made me dream of Jun last night. Ink and wash came from the other side, corresponding to the contrast, and the idea was ingenious.