The Underdog Doctor

The protagonist's girlfriend is kidnapped. In an attempt to save her, he falls from a building along with the kidnapper, and they both die. Unexpectedly, he wakes up in a parallel universe, inhabiting the body of another version of himself. His girlfriend is still alive and is now his wife, but he is just a useless live-in son-in-law. The protagonist realizes he has a great opportunity to make his mark and decides to achieve his life's potential once again in this new reality.