Yes. I've read about this in an article. It is said that when you laugh you burn calories. I just don't know if it is proven. According to scientist, laughing intensely for a 10-15 minutes a day burns 10-40 calories. I hope this is true.
I don't know about it being equal to a high-impact workout, I can see it doing something to burn calories but nowhere near the impact of an actual exercise. In addition, it's hard to find material to sustain your laugh at a regular interval.
I had commented in one discussion that watching a comedy movie that can make you laugh can burn more calories than watching a horror movie that will only give you stress and even haunt you in your sleep. Do you notice that when your laugh is roaring that you tend to sweat? Think if that moment would be repeated every minute or so, it is like doing a workout with the sweat that you will shed.
Laughing is a natural way to exercise the jaw and body muscles which can help us lose weight,it is clear that whatever we do with the body,no matter how little it is we are expending energy i.e burning calories and it is recorded that laughing for 10-15 minutes one can burn about 40 calories, so doing this often means we might burn good amount of calories which will aids faster weight loss.
I have seen in TV that there are "work out" that incorporates "laugh theraphy" to add a little calories that can be burn. In one of my yoga class, we also did a laughing yoga class to sweat a little bit more. I was not able to ask the trainer how does it work in losing weight. Maybe it does burn calories.