The Dreamlands are a vast, alternate dimension that can only be entered via dreams. They are divided up into several sections, all of which are inhabited by monsters who serve the idiot elder god Azathoth. These creatures seek to enter our world and conquer it, using human beings as a focal point.
When a human goes to bed, they eventually enter a mode called REM, which is the deepest and most important mode of sleep. This is where they gain the most rest, recharging them for the next day. Unfortunately, it is also the point that they are most vulnerable. All humans dream in this state, their minds entering the dreamlands for a period of time. This leaves them open to predators, who can consume their minds and inhabit their physical forms, allowing them to cross over into our world and enslave us. This has become more frequent, and these creatures are difficult to kill, slaughtering entire families and communities before being brought down.
The only way to prevent this is to cut people off from the dreamlands by stopping them from dreaming entirely. However, eliminating REM would lead to a lot of irate people getting into fisticuffs in the day due to lack of deep sleep. How can I do this without damaging REM mode?