I lost my father, my husband and my mother all within 10 months of each other.
The hardest part of the whole thing were the 'might-have-been's' that I still beat myself up with. What if I had pushed my husband to have that bladder biopsy that might have found his cancer before it spread to his bones and lymph nodes? What if I had gotten my father out of that horrible nursing home before he suffered a stroke, and then, as a result of sitting off balance due to the stroke, got a bedsore that went all the way to the bone? WHY wasn't I more proactive??
I am still haunted by my last visit with my dad. He was lying totally naked in bed from the waist down: no diaper, not even a sheet overtop of him. The flimsy disposable pad underneath him was soaked with urine, as was the bed, and his shirt tails. (He was wearing only a shirt and undershirt.) I was in the room for over an hour, and no one came near him to check on him. I finally went out into the hallway and tagged a nurse who was passing meds, and begged her to send someone to help change him, as he would panic and latch onto the bed rails with both hands when you tried to turn him, so I couldn't do it myself.
In the end, I had to forgive myself for what I felt were my shortcomings, and move on. My intervention would have changed very little, anyway. When the doctor finally DID do a biopsy on my husband, he still did not find the cancer. It was finally found when he examined cells he'd washed out of the bladder. My dad was 89 years old when he died. He still would have developed dementia and died in another nursing home, no matter how good it was. He might have died with more dignity, but he STILL would have died.
I have been through a very long healing and grieving process. I did eventually return to nursing after dealing with my parent's estate, but found that coming home to an empty house at the end of a shift was just too depressing. I handed in my resignation about a year and a half after my husband died. I miss being able to help people and make a difference in their lives, but I sure don't miss the stress!
Get counselling. I had both secular and religious counselling, and completed a grief and bereavement course. Give yourself time to heal if you can (a leave of absence would be a good idea, if you can get one.) See if your workplace will offer counselling, or refer you to someone who can do it. In my experience, therapists are better than psychiatrists, as the seem to have more empathy and are less wrapped up in the medical crap of brain waves, chemical recations and drugs. One very excellent counsellor I saw was an MD with special training in counselling and psychotherapy. He was marvellous, and he also respected me for the work I did as a nurse.