I think the poster is talking about waves in regard to the sleep cycle.

Beta waves occur during waking hours.

Alpha waves occur just before sleep occurs.

Theta waves characterize the first and second stages in the sleep cycle. This is when you have first fallen asleep. It is easy to wake up. This might be when you are just dosing in class.

Delta waves categorize sleep stages 3 and 4. This is deeper restorative sleep.

Lastly is REM sleep (rapid eye movement). During this stage is when you dream the most. This is also the stage in which sleep paralysis occurs yet the brain is extremely active.

I'm not sure what you mean by blocking the theta waves. Because if that was happening, you wouldn't be able to fall asleep. In addition, ADHD medication affects neurotransmitters which work on the central nervous system. I believe sleep would be considered part of the endocrine system. The two systems are related but the first works with electrical impulses and action potentials and the other with hormones.