Energy Failure

[Es.Ell.]

Hi Nisa. Loving your Mod. Last night I bought 2 Dolls from Tam Explorer. After a little while of doing stuff with them, I sent them to bed.  They're needs were ok (not in yellow zone). After a few mins of sleeping, I noticed they each had a Pink "Energy Failure" [Z Z] bubble pop up as their next activity to do after they're sleep was over. They're normal Pink "slave" Social Bar was 98% full. When they woke from sleeping, they immediately collapsed on the floor. They woke up a short time later as if nothing had happened. Sorry, as I don't know what this represents, and wanted to know how to prevent it. Thanks