Alarm doesn't always work.

I've recently began having problems with my alarm not going off in the morning.  My phone is NOT on silent and I have the alarm settings set to go off everyday.  But sometimes it just doesn't go off.  Then when I wake up late, if I look at the alarm settings, it says the alarm is set to 'ON' so I can't figure it out.

Interestingly, today after reading some of the other forum discussions, I got into my sound settings and changed my alert tone to silent and then back to ring (just messing around b/c I'd never found that option before) and then my alarm went off 25 minutes late.  Weird?