Canon 6D mirror getting stuck after taking picture?

Hello, the viewfinder on the Canon 6D stays black after I take a picture. I guess the mirror gets stuck? I try to focus, but it can't. When I change to video mode I can see everything with live view, but when I change to photo mode I can't see anything on the view finder. To be able to see something I have to remove the lens, and put it back on. I take a picture, and it's the same. I have to remove the lens, and put it back on. Is this normal? What should I do?