I totally get the point with the brain!
For many years already I only fall asleep when I have absolute mental silence for about 10 minutes, which is really much.
A decade ago I would simply go to bed when I was tired and falling asleep would happen naturally but at some point this didn't work anymore.
From my experience it is simply an overall sign for us to stop thinking too much altogether and return more to Heart-based living in the Now free from apprehension about past or future. Letting go worries, conscious ones and ones we are not even aware of as they got buried too deep in our subconscious. Incrementally, our mental body will get lighter and lighter...