Hint: This is where a short custom message from the plugin will appear. Probably because you clicked a ‘Whats This For?’ link within your website, where the plugin lives. If you require further support, we will need all the long custom messages from the plugin in your WordPress website Administration area.

Sleep status is a plugin feature that allows the plugin to exist in all websites in all environments in all life-cycle scenarios … and be what ever it needs to be. Some scenarios require the plugin features to dormant but still open to security updates, while others require it to be 100% active and ready-for-action (pun intended). The website administrator can choose. 🖖
Your WordPress Administration area shows this Notice Code (NC).
Only logged in Administrators can see it.
The plugin has a main On / Off switch for its primary features and tasks (Track, Limit & Action); that allows a website administrator to comfortably know when the plugin is active and minimising its footprint (Code & Memory) because it is mostly dormant.
When Sleep status is On then Track, Limit & Action status will always be Off.
This is a safety-net configuration available for all stages of a websites life-cycle.

The WordPress documentation recommends that deactivated plugins are also uninstalled, to remove the existance of a codebase that might be exploitable because it is not actively recieving updates. Ok, true … but this perspective does not consider the nuances of a website administrators journey through out the entire life-cycle of their website.
Plugins with a Sleep status allow quite a few of these scenarios to come-to-life; especially when exposed to system, environment and landscape information for a known organisation.
For Example: A Landscape Tiers plugin who’s primary existance is to quietly live active in a Production website backups, and come to life through Tracking, Limits & Actions when the backup is restored … has no real place being a permanent capability in non-production systems the first time through an organisations deveopment and delivery life-cycle.
When a features life-cycle first travels up throught the tiers (from Development to Test to Production) then the environment setup is quite specific and generally does not need to protect itself from Production, or protect Production from non-production environments.
However, when the Development & Test environments are intentionally created from a Production backup, all bets-are-off, because the very first WordPress endpoint request runtime execution is 100% configured to be the Production system. Which is a major problem for the real production system services and data if they are available and can be connected to, from this restored backup (aka Production Clone).
Like the wp-config.php database user and password is probably still a valid working connection to production resources from this non-production system. Which is a massive Uhh-Ohh … until someone gets around to changing that. Opps, too late, the damage is done because the freshly restored backup could be triggered by any number of background activities, a single frontend page visit, or even just the login page. Yep … you will be causing unnecessary issues if you do not proactively block important aspects of standard WordPress behaviour before that first WordPress endpoint request is triggered.
Which is why every WordPress Production website needs a Landscape Tiers plugin; and that plugin needs a Sleep feature to play-nice in each tier of the organisations landscape.
My brain is stalling … this adventure is a different kind of fun.
🖖
Quit status makes all plugin features disabled.
Sleep status makes most plugin behaviour dormant.
Track status allows quiet tasks to happen.
Limit status allows passive tasks to happen.
Action status allows aggressive tasks to happen.