My guess is that while meditating you had an accidental astral projection, which led to an out of body experience. It happens sometimes. What you need to consider is how you felt during and after you saw the entities surrounding you. What kind of energy did they emit towards you. Did you feel at peace? Did you feel power? Did you feel energized? Did you feel drained? Did you feel terrorized? Remember the difference between feeling terror or feeling panicky and fearful because you don't fully understand what's happening. Once you assess how you feel, you will know which direction to take.
Also as many have suggested, find a way to shield yourself at all times. Use a charm, a crystal, a picture of something you believe will protect you. No you are not under attack. But you seem to have opened yourself up. And this is a good thing. But with the good also comes the bad. No harm in being careful.