Okay I've had this happen to me twice now over the past week. It seems that periodically my notification sounds will stop. I will see that I have new emails but never heard the sound. I will then go send myself a test text message and it will vibrate but make no sound. I've made sure all my volumes are up, and even went in to pick a notification sound and it will work fine in the sound chooser when I pick it. I also noticed both times that it did this if I go in to Spare Parts or Battery History and look my phone is staying awake and Android Usage is the one with the partial wake lock. Generally I don't have any sleep issues, it only happens when my notification sounds have also quit working. The only way to fix it is power off and back on and then all is good again. Has anyone else experienced this?