Srimad Bhagavatam — Ekadasha Skandha, Shloka 18
Guṇa-vibhāga: The Three Modes and the Path Beyond Them
सीदच्चित्तं विलीयेत चेतसो ग्रहणेऽक्षमम् । मनो नष्टं तमो ग्लानिस्तमस्तदुपधारय ॥ १८ ॥
sīdac cittaṁ vilīyeta cetaso grahaṇe ’kṣamam mano naṣṭaṁ tamo glānis tamas tad upadhāraya
当更高的觉知衰败并最终消散，以致无法专注时，心识便崩坏，显现无明与抑郁。应知此为无明之性（塔摩斯）的主导。
FAQs
It describes tamas as producing dejection, mental dissolution or inability to comprehend, a sense of the mind being lost, and dull fatigue—signs that one is under ignorance.
In the Uddhava-gītā section, Kṛṣṇa teaches Uddhava how to discern the three guṇas by their effects on consciousness so a seeker can recognize conditioning and move toward transcendence.
When you notice persistent dullness, inability to focus, and heavy lethargy, label it as tamasic influence rather than your true self, and consciously shift toward clarity through sattvic habits and devotion.