The phrase "to become sluggish" means to slow down or lose energy, becoming less active and more lethargic.
Sentences with «to become sluggish»
At this point, some cats also begin acting mildly ill, such as becoming sluggish and refusing to eat. (vetinfo.com)
The thyroid can become sluggish in many ways, many of which will not show up on tests your doctor performs. (myersdetox.com)
In our brains, this translates to more sugar being needed for us to release happy hormones like serotonin, as our brains become sluggish and less productive. (dietselfhelp.com)