It sounds as if you drifted into the hypnagogic state, the borderland between waking and sleep. Presumably listening to the binaural beats was putting you into an alpha or theta state.
The pulling of the arm may have been the beginning of an out-of-body experience, where some force was trying to pull your astral body out of the physical. Hearing random voices and sounds is typical of the hypnagogic state - these can be very loud, which can be strange in an otherwise quiet room.
These are not unusual events, but normally we just fall asleep without being consciously aware of the process. If you are serious about developing your meditation practice then you might want to sit upright on a cushion - you are less likely to drift off.