Depending on whether this was a dream or not it may have been SP or hypnogogic hallucinations. If it was a dream then it was probably just the dream fading and you returning to your waking body, something I've experienced as well. However, if it wasn't a dream then it may have been SP or a form of hypnogogic hallucinations. During SP people often report intense vibrations as they get closer to falling asleep and this may be what you're talking about. However, the part where you said you could move, just slowly, makes me think it was a form of HH. People normally think of HH as seeing images or hearing sounds but they can also include feelings and sensations. For HH you don't have to be in SP, just close to sleep or in a very relaxed state. No matter the case it shouldn't be anything you worry about and you were right not to be scared .