"Mental lethargy" refers to a state of sluggishness or laziness of the mind, where a person lacks motivation or energy to think, learn, or engage in mental activities. Full definition
The syndrome manifests itself in pain and tenderness in deep tissue and muscles, leading to bouts of fatigue, interrupted sleep and mental lethargy in many sufferers. (advocatedaily.com)
If you are fairly lean or, in the deeper phases of dieting, you are more susceptible to metabolic adaptation and mental lethargy. (fitnsync.com)
It's not surprising that cold showers have been shown to improve depression, anxiety, and mental lethargy. (drjockers.com)