Here is a problem that I regularly face:

I have a hard time terminating certain subroutines in my brain. This most regularly happens when I am thinking about a strategy game or math that I am really interested in. I will continue thinking about whatever it is that is distracting me even when I try not to.

The most visible consequence of this is that it sometimes interferes with my sleep. I usually get to bed at a regular time, but if I get distracted it could take hours for me to get to sleep, even if I cut myself off from outside stimulus. It can also be a problem when I am in a class that I find less interesting that whatever math I was working on before the class.

I know there are drugs to help with sleep, but I am especially interested in a meta-thinking solution to this problem. Is there a way that I can force myself to clear my brain and get it to stop thinking about something for a while?

One idea I had is to give my brain another distracting activity that causes it to think, but has no way to actively stay in my head after the activity is finished. For example, perhaps I could solve a Sudoku or similar logic puzzle? I have not tried this yet, but I will next time I am in this situation.

Any other ideas? Is this a problem many people face?