When on account of the organs being fatigued, they cease to discharge their respective functions, the owner of those organs, their action being suspended is said to sleep.
इन्द्रियाणां स्वकर्मेभ्यः श्रमादुपरमो यदा। भवतीन्द्रियसंत्यागादथ स्वपिति वै नरः॥