Flatliners (1990)

Kiefer Sutherland (I think...pretty safe guess, anyway) is part of an all-nighter-pulling team of scientists who discover that they can maybe bring people back from the dead, and a few of them—maybe all?—try it, after which I think they start having terrifying visions, like they brought something back. Then it turns out they just have to go around apologizing to people they wronged as kids. Oh, maybe one of them can't do that because the person he wronged committed suicide? Not sure what happens then. Nothing too cheerful, I'm thinking.

Also starring—Oliver Platt, as "Igor."