Temporary Sleep

I was reincarnated as the head knight of my kingdom only to find that I had been captured by my enemy! Forced to fight for my life I was suddenly reminded what living really means. but- there's only one thing whenever I sleep in the real world I get sent to a fantasy world and when I sleep in the fantasy world I'm sent back to my world. How will I learn to fight for my life in this new world filled with swords and sorcery?!