1 Gita Sloka Every Day - Chapter 18 - Moksha Sanyasa Yoga - Sloka 39

The entire content of this mail is from Shri V N Gopala Desikan's  Srimad Bhagavad Gita, published by Vishishtadvaita Research Centre, Chennai and The Bhagavad Gita by Swami Chidbhavananda published by Ramakrishna Mission

The grades in the firmness of mind are being described now:

The Three Gunas Give Impetus to Karma - 18-40

1 Gita Sloka  Every Day - Chapter 18 - Moksha Sanyasa Yoga - Sloka 39

Yat agre cha anubandhe cha sukham mohanam atmanah I

Nidra alasya pramadottham tat tamasam udahrutam II sloka 39

यत् अग्रे च अनुबन्धे च सुखं मोहनं आत्मनः I 
निद्रा आलस्य प्रमदोत्तम तत् तामसं उदाहृतं II  स्लॉक् 39

That happiness which deludes the self both at the beginning and the at the end which arises from sleep, sloth and miscomprehension - that is declared as tamasika

A man derives happiness from intoxicants that make him forget the miseries of the world temporarily. But this happiness is wrought with misery in the procurement of stuff, in the consumption of of it in privacy, in being exposed to ridicule when tipsy and in getting sunk in spirit after its effect wears off. The lazy man who seeks to maintain himself with borrowed money meets with the same fate. His happiness is marred while borrowing, while expending and while trying to clear the debt with great effort. Sleep and repose are necessary to all embodied beings. There is immense happiness too in indulging in them. But the sattvika and rajasika men shake off sleep and sloth at the call of duty. Whereas the tamasika man delights in prolonged sleep and in dozing for hours together. But this happiness is nullified by the neglect of duty, by the pricks of conscience and by the derision of the active people. The tamasika man often suffers from miscomprehension in regard to the means of the procurement of happiness. Like a flash of lightning his happiness comes and goes.