I've started doing meditation about a week ago.In the begining days,i was feeling great and my mind was getting clearer.But today when I tried to meditate,i felt like my whole body was trembling.I asked my bro to watch if i was really trembling,but he didn't see me trembling.I also heard a sound after my body started trembling.I got scared and immediately stopped doing meditation.I searched in google and found that some people have experienced it too. why does it happen?