Lassitude

[Sarah]

A condition of the body, or mind, when its voluntary functionsare performed with difficulty, and only by a strong exertion of thewill; languor; debility; weariness.The corporeal instruments of action being strained to a high pitch .. . will soon feel a lassitude. Barrow.

[Sarah]

A total and completly lack of energy, a state of physical or mental weariness.

[Sonia]

physical or mental tiredness:

[Julian]

A state of physical or mental weariness; lack of energy.