That just means there is an inverse relationship between the two metrics with a lag between the first and second metrics. The lag time can amount to one day, one week, or one month, depending on which chart view you’re using.
Here’s what it looks like:
This chart means that if you sleep more today, your risk of overworking will be lower tomorrow in 75% of cases.
And if you sleep less today, your risk of overworking will likely be higher tomorrow.
If you see a correlation like this, the insight is pretty straightforward — getting less sleep puts your body’s systems under a ton of pressure, making it more likely that you’ll end up pushing past your limits that day.