What Causes Swelling In Foot And Sleepiness Post Stent Implantation?

My mom had a stent put in her heart. Before she went the hospital she was just fine. Although it was her second one she had one about ten years ago put in.when came home from the hospital she had a swollen foot and breathing complications. And she would fall asleep at the drop of a dime. Never had she done that. The next morning i found her on the floor she looked as though she fell straight out her chair. Her fist was balled up. She had passed away. Can someone please tell me what might have happen?