Have you ever gone into a meditation with high hopes of reaching the great, deep, peaceful, distraction-free space that you got to yesterday or last week? It's probably safe to say we've all been in that position. Sometimes we just can't get there, and that's OK too.
Personally, I don't think there is anything like a “bad” meditation. Even a meditation session that was a bit on the shallow, distracted, or superficial side would nevertheless still be 20 minutes of quiet time and stillness, a gift in and of itself. If a particular meditation experience turns into one long planning session, there were likely a few times where the brain got exercise by bringing attention back to the breath. If it is particularly hard to stay seated, it’s progress to stay with it for just a bit longer, no matter how long.
It is important to remember that meditation requires practice. Why do we practice? Because proper meditation takes effort, discipline, and concentration. It is a learned skill that must be honed and maintained. If meditation were just as simple as closing your eyes and breathing than it would hardly be something worth attaining. The entire point of meditation is that it is a special time. It is sacred. It isn't a common phenomena or feeling. It is something to be attained or earned.
Some days just can't be “winners.” This is a fact of life. Consider a poor meditation session as another opportunity to practice the basic principles of meditation—acceptance, mindfulness, self-awareness, etc. You can even use it as an opportunity to take your next session more seriously, if that is the right word. Learn from the session you are unhappy with and focus on what can be improved for next time.
~ Jillian Avey, purelifemeditation.com