My 6 mth old Border Terrier urinated in his sleep! He was castrated 10 days ago - is there a connection?

He was lying on back asleep in his little bed having an afternoon nap when he just completely wet himself. I was quite shocked. He's not done this before he was castrated. I was very careful for 10 days not to overexercise him, let him jump up etc and he wore his funny little lampshade shade thing round his neck the whole ten days. His stitches were taken out today and you can hardly see the scar. Has this happened to anyone else? Many thanks for taking the time to read my question :)