On July 21, police say, Mercado cut in line in front of Douglas Seyfried at the New Directions Treatment Center in Bethlehem Township.
Police say the two then started yelling at each other. After they received their treatments, officials say they started pushing and punching each other in front of the clinic.
Investigators say Seyfried didn't realize he had been stabbed until he felt pain in his side while driving a short time later. He was treated in the trauma unit at Lehigh Valley Hospital.
Mercado's defense attorney says his client suffers from bi-polar disorder and depression.
Information from: The Express-Times, http://www.lehighvalleylive.com