Deeply buried in the mind, there lies a mechanism that accepts what the mind experiences as beautiful and pleasant and rejects those experiences that are perceived as ugly and painful. This mechanism gives rise to those states of mind that we are training ourselves to avoid-- things like greed, lust, hatred, aversion, and jealousy.
Let come what comes, and accommodate yourself to that, whatever it is. If good mental images arise, that is fine. If bad mental images arise, that is fine, too. Look on all of it as equal, and make yourself comfortable with whatever happens.
Mindfulness gives you time. Time gives you choices. Choices, skillfully made, lead to freedom. You don't have to be swept away by your feeling. You can respond with wisdom and kindness rather than habit and reactivity.
Mindfulness helps us freeze the frame so that we can become aware of our sensations and experiences as they are, without the distorting coloration of socially conditioned responses or habitual reactions.