I was absolutely exhausted and just wanted to go to bed, but my fluffy cat, Sir Paws, had other plans. He was sitting right in the middle of the bed, glaring at me like I was an intruder in his kingdom!

We use the zero article (no article) for the abstract idea or intended purpose of the noun ("go to bed" means "to go to sleep").

We use the when referring to a specific physical piece of furniture ("the middle of the bed").