When players use downtime to rest and refresh, you gain Fear and can progress a countdown happening in the background:

• On a short rest, gain 1d4 Fear.
• On a long rest, gain an amount of Fear equal to the number of PCs + 1d4 and advance a long-term countdown.

This helps make the world feel alive—and it reminds players that the more resting they do, the more the world moves without them, so they might want to be careful how much they rest.