The only way to find out is by dying. When solely taken from scientific point of view... nothing, just nothing. Officially called "eternal oblivion". In a more philosophical way of thinking we know that in nature everything is recycled. So what happens to your conscience? Is that recycled as well? If so reincarnation can suddenly be plausible. The "Deja vu" phenomenon is often credited to reincarnation. The point is, since I ain't dead, I don't know.... And once I'm dead, I can't tell you about it.... Those are the only facts I have....