Sleep Tight - S3-E16
Continuity mistake: Right before Holtz and his men arrive at the hotel, Angel arranges three of Connor's toys in his cot. One of them is a teddy bear which he places in the middle of the cot. But once Holtz and his men arrive, the teddy bear is suddenly at the far end of the cot resting on the pillow.
Sleep Tight - S3-E16
Revealing mistake: When Angel is seen gulping the blood from the cup (right before Lorne tells Angel that Connor needs some papa-love) you can see this is a special-effects cup (it's like one of those freezer mugs, where there's a layer of liquid on the outside). If Angel were really drinking out of the cup the way it's shown, he would have blood all over his lips and it would be running down his chin.
Sleep Tight - S3-E16
Audio problem: At the end of the episode when Holtz jumps into the dimensional rift with Connor, we hear Angel yell "no" twice. But his lips don't move on either occasion.
Answer: Due to his epiphany, Angel basically had the 'true darkness' he worked so hard to reattain ripped away from him, like his soul was after sleeping with Buffy.