I'd say it means your neck is stable. It has ligaments that hold the cervical vertebra in place, even when the muscles are completely relaxed. For people who have unstable necks, they need to maintain good sleeping posture so they do not strain the ligaments and cervical vertebra alignment while sleeping. This good posture allows the ligaments to strengthen/tighten so they properly support alignment.

If you are maintaining alignment, your misalignment was likely minor and stabilized quickly.

Not everybody with a concussion has an unstable upper neck.