I didn't memorize the route from the interrogation room to my cell. There are hardly any reference points in here and if you don't have an eidetic memory or are good at remembering the permanent left, right, left, right in order to act it out backwards later, you are lost in these tunnels. Also, I was too tired after the first questioning. So I can't say for sure if it's the same door that Potter is holding open for me now. At least it looks like the same. So maybe it's the same chair I drop into and maybe it's the same table I put my hands on. 