What would cause temporary halo bulb outage?

[RenaissanceMan]

Late last week I started getting the 'check side lights' message in the dash, and then verified that my driver's side halo bulb was not working. This happened a couple of years ago on the passenger side and after replacing the bulb all was well. I planned on picking up a new bulb for the driver's side this weekend but today I noticed that I wasn't getting the 'check side lights' message anymore and a quick check up front revealed that the halo bulb was working again. What would cause an intermittent bulb outage like that? I have an '05 X5 with xenons. Thanks for any insight-