Is moving from a 20 gal to 10 gal mean?

My 4 year old betta fish Annyeong lived in a 10 gal tank his first couple years, then upgraded to a 20 gal. He is older and literally only swims on one side of the tank, hangs out at the top, sleeps a lot, not that active (hopefully just cuz he’s old).

Would it be mean to put him in a 10 gal tank again so I can move the tank to a more convenient place in my apartment? Will he miss the space? Maybe he uses the other side of the tank when I’m not there? Has anyone else done this before?

Thanks!!!!!