Disable sleep in macOS
Semiphemeral runs directly on your computer. If you need to run it for hours or days (X has some annoying rate limits, so this is likely), you should prevent your computer from going to sleep while it's working.
The simplest way to prevent your Mac from automatically going to sleep is to use Caffeine, a tiny free and open source app.
Download and install Caffeine from https://www.caffeine-app.net/. When you run it, an empty coffee cup icon appears in the top-right of your menu bar. Click it (the icon changes to a cup full of hot coffee) and Caffeine will prevent your computer from sleeping. Click it again to disable it.
Now you can safely run Semiphemeral for an extended period of time.
Note that your Mac will still go to sleep if you close the laptop lid. So, don't close your Mac while you're doing a long-running Semiphemeral session.
Remember to disable Caffeine when you don't need to use it.