Alarm didn't go off after hitting snooze...

... And when I say it "didn't go off" I mean it didn't alert me after the 9 minute snooze period.

I use the default clock app for my alarm. Last night I told Siri to wake me up at 6:45am, and she's been good to me so far...

It initially went off as it was supposed to, at 6:45am this morning, I hit the snooze button, fell back to sleep, and then woke up when I heard my roommate's TV around 8am. I then checked my phone, saw the time, sent my boss a text to let him know I'd be late, and got ready for work. While I was getting ready, my alarm started to ring again, probably about 9 minutes after I woke up (the second time) and checked my phone.

I'm wondering why my alarm decided not to work when the screen was off. It seems like turning the screen back on and/or unlocking it put the alarm back on the snooze schedule. I think I remember unplugging my phone from the nightly charge when the alarm initially went off at 6:45, and I may have gotten a notification from either CNN or Battery Doctor. I'd like to know if anyone else has had an issue like this, and if hitting snooze, then going into another app, had anything to do with it.

Any help would be appreciated, I can't have this happen again!