Sleep mystery explained

Every day for the past week and a half I have been waking up inexplicably at around 4:30 in the morning and quickly falling back asleep after a walk over to the bathroom. Initially I put the blame on my bladder, but last night I uncharacteristically slept without a watch on my wrist. This morning I had to get up and find the watch to shut off the 4:30 alarm I must have set last Sunday to make sure I don't miss my race. Apparently I have been waking up and turning off the alarm without noticing, and going back to sleep every morning since September 19.