Canonically, we are shown very little of Shepard's true condition when they scrape her off of Alchera; we know that her remains were taken by Blue Sun and that the Illusive Man teamed up with Liara T’Soni to keep the Shadow Broker from taking her, and then Cerberus threw a gajillion credits into reviving her. The extent of this damage is only really explored in detail in the Lazarus Project cut scene (link), wherein you can see extensive tissue death, nerve damage, and bionic implants.
At around 25 seconds in, if you can still the frame, you can see Shepard’s skeletal structure, which is deeply lacking. Almost all of her ribs are broken, her right arm appears to have been completely severed (or at least the bone is), her shoulder blades are shattered, her spine is missing some pieces down at the bottom near the pelvis. Most of her right arm and left leg appear to be missing. At 45 seconds, you can see them inserting a spinal implant, and directly after that shot is one showing all the splints they put in, along with areas of interest, which are considerable. They were able to regenerate a lot of her tissue, but bone wasn’t really an option for that, so a lot of Shepard’s bones are metal (or otherwise synthetic).
When she first wakes up, in her conversation with Jacob, he says, “I’m no doctor, but it was bad. When I first saw you, you were nothing but meat and tubes. Anywhere else, they’d have put you in a coffin. But Project Lazarus was different. Cutting edge technology... You’re still you; you just might have a few extra bits and pieces now.” (link) In ME3, there is an opportunity to learn just how dead Shepard was (link), when she finds video records of the project and learns that she was medically dead, brain dead, and for a lengthy period of time. Up until then, she had never really understood what happened. She always played it off as being rumors or just a really bad coma, but eventually comes to realize that she was legitimately deceased for a while, and the two years it took to bring her back take on a new meaning for her.
What’s interesting about Shepard’s relationship to her own mortality is that she was never really afraid of death until she actually died. The last time she can remember feeling horrified by death was on Mindoir when she was sixteen, and she was so overwhelmed by what was happening that she couldn’t really fully process it. Afterwards, she became obsessed with fighting the people who had destroyed her home colony, and a large part of that included death, so she became kind of immune to looking at it from a very early age. That combined with the survivor’s guilt she suffers not just from Mindoir but also from Torfan, and really Shepard has been ready to die for years. When she realizes that she actually did die, it fucks her up because she doesn’t remember it at all, and it calls her faith into question because if she was really dead, she should have been with her family when she died. Then she decides that she didn’t see her family because Cerberus recovered her too quickly, and she feels robbed of her eternal resting place, and that’s why she’s comfortable with a suicide mission.
As I’ve mentioned before, it’s not that Shepard is suicidal, per se, but that she has always felt that she shouldn’t have survived the raid on Mindoir and that she’s on borrowed time. She shouldn’t be alive, and she doesn’t really want to be, and the only time she feels alive and in the here and now is when she’s fighting, and when she’s with Thane. Surviving the attack on the Collector ship was only really acceptable to her because she knew the Reapers were coming, and putting civilian lives before her own wellbeing is deeply hardwired in her mind. After Earth is attacked and Thane dies, it becomes harder and harder for her to keep going, so she gladly sacrificed herself to the Crucible, believing fully that she would die (especially since she’s so synthetic by then??). Her survival past ME3 is a pretty dark area of her timeline and it's gone largely unexplored.












