I really don't know either. I always thought it sounded like (from near death experiences, etc.) that you instantly just started passing into afterlife, going where ever you're going. Also I think I read something in Buddhism that it takes 40-45 days for this passage to occur.
Either way, I never thought there was a period of null-like sleep, awaiting judgement, but recently have read that too in Christianity. So I don't know. It also adds to confusion when people say their loved ones have passed and are in heaven. Sure, you want to believe that, because otherwise, where are they?