I accidentally clicked on the option "When power is critically low" under System Settings>Power. The original entry was blank, but the only two options after I clicked were Hibernate and Shutdown. I want to set it back to Suspend.
There is no option to suspend available.
You cannot suspend when power is critically low, to suspend you need power to save the session to RAM allowing you to resume quicker, if you loose power you loose the current suspend state.
Hibernate copys the current state to the hard drive, it is slower but you can turn off the power.
Shutdown is obvious - you will loose any data in the active session and have a new session on restart.
To change this setting back to suspend, use dconf-editor. Go to org.gnome.settings-daemon.plugins.power and change critical-battery-action to suspend.
Alternatively, in a terminal session use the command: