Yep, absolutely nothing to worry about. What you are experiencing is exactly what I described. These vibrations typically occur when in between awake and asleep, so normally this is either shortly after turning the lights out, or in the early hours of the morning as you start to awake from a deep sleep. Paralysis of the physical body during this is also the norm and, yeah, it can also freak people out who don’t know or understand what is going on.
But it is a great thing! In fact, many people spend months, or even years practicing meditation and visualisation techniques specifically to achieve this brain state in their waking hours in order to astrally project/soul travel.
So, yeah, next time you experience this don’t waste the opportunity. Go with it and then imagine rising out of your body. I won’t spoil the surprise of what will happen, but it is fantastic and will leave you wanting more. It will also most probably change your perception of who you really are. Enjoy!