Do you work at a vet's office?
I work at an animal shelter. We work with 3 different vet's offices, and we've had hundreds of animals spayed/neutered since I've been working at my job (and we've had almost no major complications with these surgeries!)
To be perfectly honest, I can't remember which vet told us this theory, but we have seen a lot of young male dogs that have an intense increase in energy and inappropriate behaviours following surgery, and they've all gone back to normal after 3 weeks. It's very interesting!