Her character had seemed to overcome all of the demons of her past as she worked on her career as a cop, but Erin Lindsay's fall from the top during season 2 of Chicago P.D. was something Sophia Bush admits was tough for her as well. 

Linsday Spirals Out Of Control In Season 2 Finale Of 'Chicago PD'

In an interview with The Wrap, Bush admitted that filming Erin's struggles after Nadia was murdered by a psychotic serial killer during the special crossover episodes with Chicago Fire and Law and Order: SVU was by far the hardest thing she had to do all season, because of how much she had to put into her performance so she too would believe it.  

"The toughest thing I had to do this season was having Erin unravel in such an extreme way very quickly following the death of her friend," Bush said. "I had to wrap my head around her behaving in ways that she spent a lot of her life walking away from. And from those kinds of habits. I had to create an arc that made a backslide so drastic make sense for me, and hopefully for the audience." 

Sophia Bush & Jesse Lee Soffer Break-Up

However, Bush also admitted that she did have some fun during the hard season, and even got to perform her own stunts.  

"By far one of the coolest I got to do all year was film this high speed chase across Lake Street in Chicago," she said. "We had about a mile of the street shut down. It's usually teams of stunt drivers doing the driving, but they've all gotten to know me, and they know that I've become quite the amateur race car driver myself. And they let me do all of my own stunt driving on the show." 

Bush returns on season 3 of the show this Fall.