Both Physical and Psychological
My Thematic Statement
O'Brien smiled again. "She betrayed you, Winston. Immediately-unreservedly. I have seldom seen come over to us so promptly. You would hardly recognize her if you saw her. All her rebelliousness, her deceit, her folly, her dirty-mindedness-everything has been burned out of her. It was perfect conversation, a textbook case. "You tortured her?"
This proves the Julia had gave him up easily and his demise followed shortly after.
2) He had stopped because he was frightened. A bowed, Grey colored, Skeleton-like thing was coming towards him. Its actual appearance was frightening, and not merely the fact that he knew it to be himself. He moved closer to the glass.... At a guess he said that it was the body of a man of sixty, suffering from some malignant disease. It was himself.
This just goes to show how he broke down after seeing himself in the glass. He then told everything the next time the officers had come to him. The psychological part of him gave it all up, after being betrayed and now seeing his image in the glass, it proved to be to much for Winston.