We are always in motion, even when sleeping, resting or napping. Why? Our bodily chemicals are always moving. And our body actively is rebuilding while we sleep and rest. To sleep much is also a virtue in body building, muscle building, strength building.

What is death? When our bodies no longer move — either internally or externally. No more breathing.

Source—

Plato, Theaeet. 160d .
Homer, and Herakleitos, and the whole company which say that all things are in motion and in a state of flux. Cf. 152 D. H.
Plato Kratylos, 401d.According to Herakleitos all things are in motion and nothing abides.Cf. 402a, and frag. 41; also 412d, 440c.