This has only happened once, but then it's the only time I've been shot in the head.
I was shot wearing a pristine ballistic helmet and went unconscious. When I woke up, I noticed the texture on the helmet had changed, and it displayed as "badly damaged".
Some time later, maybe 15 minutes, while still in the same server session, I realized the helmet texture was back to normal and the status displayed as pristine again.
This may not be 100% related to the helmet, but it's the item I noticed it in, and I dropped everything else that became ruined when I was hit.