If you killed someone accidentally and its was over a year ago can you still sleep at night?

I very much doubt it. That would haunt me for years. Even with meds and therapy. That's why people that have killed someone would likely never do it again. Their brains punish them far worse than prison ever could.

No. I have a hard time with guilt over smaller things than that.

That would be horrible ... I imagine the nightmares would be unrelenting