Without knowing more about the kind of world you’ve created and assuming your characters are human beings, let’s explore this some more.
First, think about the types of injuries your character has sustained. Is there a lot of head trauma? Chest trauma? Was it blood loss? Was it something that shocked him and caused his heart to stop? Was it smoke inhalation? The types of injuries your character sustained will help you sort some of this out. Once you get a vague idea of your character’s injuries, begin researching. WebMD and Wikipedia have good stuff, but Youtube has many videos made by medical schools for educational purposes. Just so you’ve been warned, the videos and pictures are graphic.
Necromancy, using magic to revive or reanimate the dead, is not without limits and repercussions. In the Greek and Roman tradition, reviving a person involved shoving their soul back into their body. Many ancient texts describe in detail the excruciating screams of the person who has been revived. Remember, just because you have been brought back to life, does not mean your injuries have healed. Furthermore, necromancy wasn’t a permanent fix. Typically, it was for a short period of time- a few moments, usually- to pass along a message or convey information then their soul would be released. Reanimation is a little different in that that person’s soul (or energy, or whatever you want to call it) isn’t involved. Up until 50 or so years ago, this is how zombies were “made”. The virus is a new thing.
If you feel comfortable doing research into necromancy (it’s okay if you don’t), I’d be wary of the internet. Daniel Ogden is a professor of ancient history in England and he’s written a number of books on magic and necromancy in Greece and Rome. I’ve read his books and I recommend them highly. Another book you may want to read is Forbidden Rites: A Necromancer’s Manual of the Fifteenth Century by Richard Kieckhefer. Basically, a university in Germany has a 15th Century necromancers manual written in medieval Latin, and Prof. Kiechkhefer translated it and added more information to it. Those books are available on amazon, but you may be able to get them through your library. If the world you’ve created aligns more closely with another culture or tradition, search on Google scholar. You’ll find better information.
Ironically, modern medicine runs into some similar issues when trying to revive someone whose heart has stopped. Lack of blood flow to the brain, for any amount of time, causes brain damage. Full stop. There are all sorts of medical procedures to keep oxygenated blood flowing to the brain to prevent further damage, but they can only do so much. In short, anything longer than a couple seconds, and you will have complications. Just as unrealistic it seems to have someone die and be brought back through magical means, it’s equally unrealistic to have a character be clinically dead for several minutes to have them make a 100% recovery. If your character miraculously survived the trauma (no heart stoppage or brain injury), do they have plates screwed to their bones or scars? It is exceedingly rare to make it through a life-threatening injury without a scratch or scar.
After you’ve done some research, write a couple pages with each scenario. This doesn’t have to be perfect, it’s just a writing exercise. When you’re done with both, don’t look at them for a few days. You want fresh eyes and a clear head. When you come back to them, think about what fits best with the world you’ve created. While realism can be a great thing, consistency is just as important. If you have magic in a world, you may need to address why they don’t use necromancy. Pick what you feel is best. Celebrate your awesomeness.
With that done, you’ve got one last thing to do. Follow Faulkner’s sage advice and “kill all your darlings.” You say you grew so attached to your character you brought him back. Write a few pages about how the other characters react to this death. Take some time and imagine how the plot and storyline will change. Walk away for a couple days, then sit and think what makes the most sense for your story. The results may surprise you.