Season 5: Episode 18

Sheldon's life is turned upside-down after his barber gets sick. Meanwhile, Bernadette (Melissa Rauch) listens to Howard explain how astronaut training causes him to rethink his decision to go into space, on THE BIG BANG THEORY. Photo: Michael Yarish/Warner Bros. ©2012 Warner Bros. Television. All Rights Reserved.

Sheldon's (Jim Parsons) life is turned upside-down after his barber gets sick. Meanwhile, astronaut training causes Wolowitz to rethink his decision to go into space, on THE BIG BANG THEORY. Photo: Michael Yarish/Warner Bros. ©2012 Warner Bros. Television. All Rights Reserved.

Sheldon's (Jim Parsons, right) life is turned upside-down after his barber gets sick. Meanwhile, astronaut training causes Wolowitz to rethink his decision to go into space, on THE BIG BANG THEORY. Also pictured: Kaley Cuoco (left). Photo: Michael Yarish/Warner Bros. ©2012 Warner Bros. Television. All Rights Reserved.

Sheldon's life is turned upside-down after his barber gets sick. Meanwhile, astronaut training causes Wolowitz to rethink his decision to go into space, on THE BIG BANG THEORY. Pictured: Kaley Cuoco (left) and Johnny Galecki (right). Photo: Michael Yarish/Warner Bros. ©2012 Warner Bros. Television. All Rights Reserved.

Sheldon's life is turned upside-down after his barber gets sick. Meanwhile, astronaut training causes Wolowitz to rethink his decision to go into space, on THE BIG BANG THEORY. Pictured (left to right): Johnny Galecki, Kaley Cuoco, Jim Parsons. Photo: Michael Yarish/Warner Bros. ©2012 Warner Bros. Television. All Rights Reserved.

Leonard (Johnny Galecki, center) is a witness as Sheldon's (Jim Parsons, right) life is turned upside-down after his barber gets sick. Meanwhile, astronaut training causes Wolowitz to rethink his decision to go into space, on THE BIG BANG THEORY. Photo: Michael Yarish/Warner Bros. ©2012 Warner Bros. Television. All Rights Reserved.