When you get up in the morning and just before sleep, you are naturally in this state. When you close your eyes your brain automatically starts producing more alpha waves. Many studies monitoring the EEG activity of experienced meditators have revealed strong increases in alpha activity.
Bottom-up processing happens when someone tries to understand language by looking at individual meanings or grammatical characteristics of the most basic units of the text, (e.g. sounds for a listening or words for a reading), and moves from these to trying to understand the whole text.
Top-down processing involves higher-level cognitive functions, such as thinking and memory, which allow us to utilize information that has previously been taken in by our sensory systems. Top-down processing allows us to avoid the need to re-experience things over and over again.