Distractions in Meditation

Upon asking questions previously, I wondered some things about my meditation. In meditation, I often experienced greatly reduced thoughts, almost no thoughts; but, the sensations at the tip of the nose are almost always lacking. **Is it possible that, despite the absence of thoughts, something other than arising cognitions pulls my attention away from the meditation object?** Just to be clear: I am asking what specifically are the type of possible distractions which may arise in meditation. I'm also wondering what is the relative strength of these distractions, for example: does a single thought break concentration? Does paying attention to some external object merely once break concentration?