Treatment of Allied POWs (at least those from the West) in German POW camps was largely professional.
Here's the text of an excerpt (7:10-7:28) from the above interview with Walter Morison, a British former POW held at Sagan and then Colditz.
For more information about his escapes and daily camp life, see his book Flak and Ferrets: One Way to Colditz.
(Enlisted men and those in larger camps probably had it rougher, especially in terms of food. Things also got considerably worse towards the end of the war -- and even in the immediate aftermath.)