Katha Upanishad Verse 1.2.21
This verse describes the paradoxical nature of the Atman (the Self). Though it appears seated or lying down, its influence and presence are all-encompassing. Its joyful and joyless aspects represent the transcendence of opposites, a state that can only be understood by a realized soul like Yama himself.
Sanskrit Verse
आसीनो दूरं व्रजति शयानो याति सर्वतः । कस्तं मदामदं देवं मदन्यो ज्ञातुमर्हति ॥ २१ ॥
Transliteration
āsīno dūraṃ vrajati śayāno yāti sarvataḥ | kastaṃ madāmadaṃ devaṃ madanyo jñātumarhati || 21 ||
Translation
Sitting, he goes far; lying, he goes everywhere. Who else but me deserves to know the God, who is joyful and joyless.

Muni's Play