Emotion in Compassion Meditation I have a very simple question. Sometimes, I visualize in compassion meditation without feeling anything for the whole session. Sometimes, I feel a lot of affect and start even crying. 

Should one focus on/have the emotional sensations in compassion meditation for it to be efficient, or is visualizing -- even without emotion -- enough?
In "Awareness Itself", we read the advice given by Ajaan Fuang, as recorded by his student Thanissaro Bhikkhu:


  § A young nurse practiced meditation with Ajaan Fuang several days
  running, and finally asked him one day, "Why wasn't today's session as
  good as yesterday's?"
  
  He answered: "Meditating is like wearing clothes. Today you wear
  white, tomorrow red, yellow, blue, whatever. You have to keep
  changing. You can't wear the same set of clothes all the time. So
  whatever color you're wearing, just be aware of it. Don't get
  depressed or excited about it."
  
  § A few months later the same nurse was sitting in meditation when a
  sense of peace and clarity in her mind became so intense that she felt
  she would never have a bad mood infiltrate her mind again. But sure
  enough, bad moods eventually came back as before. When she mentioned
  this to Ajaan Fuang, he said, "Looking after the mind is like raising
  a child. There will have to be bad days along with the good. If you
  want only the good, you're in for trouble. So you have to play
  neutral: Don't fall in with the good or the bad."
  
  § "When the meditation goes well, don't get excited. When it doesn't
  go well, don't get depressed. Simply be observant to see why it's
  good, why it's bad. If you can be observant like this, it won't be
  long before your meditation becomes a skill."
  
  § A student came to complain to Ajaan Fuang that she had been
  meditating for years, and still hadn't gotten anything out of it. His
  immediate response: "You don't meditate to 'get' anything. You
  meditate to let go."
  
  § "You should watch visions the same way you watch TV: Just watch it,
  without getting pulled inside the tube."