My iMac screen is dark and isn’t lighting up like I expect it to when I tap the keyboard. I can, however, SSH into it and see what it’s doing when not responding to me.
I found GoogleSoftwareUpdateAgent running, this FAQ item vaguely tells me it’s part of Chrome, and that if I try to uninstall it without also uninstalling Chrome it will simply “be reinstalled after a few hours.”
com.apple.iCloudHelper is using a lot of CPU (100% of one of the cores). Googling for it reveals other people inspecting their systems while the screen refuses to awaken. I’m guessing it’s related to, um, iCloud and syncing, but the interwebs don’t say much more about it and killing it didn’t fix the problem.