I can tell this, because of what happened when I woke up. My alarm clock went BEEP BEEP BEEP and said 8:00; so I hit Snooze, struggled to semi-wakefulness, and started trying to remind myself of the things that had really happened yesterday (board games, Doctor Who, washing up) so as to form a clear distinction between them and the things that had only happened in the past night's dream (awaiting trial on a technicality in the strange and fictitious legal system of an unnamed state which wasn't sure – and spent a lot of time hotly debating – whether it was religiously constituted or not). Somewhere along the line I slipped back into sleep.
Fortunately, my alarm clock saved the day by going BEEP BEEP BEEP again. But, curiously, it still said 8:00, not 8:09 as I would have expected. I could only assume that this was in fact the first time the alarm had really gone off, and the previous very realistic occurrence had in fact been part of my dream. Somewhat bemused, I went straight to the computer to write a diary entry about this bizarre phenomenon before I forgot about it.
The computer's clock said 8:12, and when I went back into the bedroom to check, so did the alarm clock. This suggested that it had in fact been 8:09 when the alarm went off the second time; so either my alarm clock has a misfeature whereby it displays the primary alarm time while beeping after a subsequent snooze period, or I'm completely unable to read at that time on a Monday morning. Neither is beyond the bounds of belief. Nor is the possibility that I in fact did dream the first alarm occurrence, the second did say 8:00, and I then dozed for ten minutes without noticing before getting up.
Something tells me that experiencing that much confusion within the first fifteen minutes is going to set its stamp on the entire day. If you catch me unaccountably talking about wombats or walruses at any point today, you'll know why.