Alasya

Alasya (Laziness):
The body and the mind is turned towards inaction, i e laziness. Even if all the abovementioned hindrances are removed, and if there is laziness, then there will be no karma or action and hence no progress.

The impediments to yoga practice, that is which create fluctuations of the chitta or consciousness are: disease (vyadhi), sluggishness (styana), doubt (samsaya), carelessness (pramada), idleness (alasya), sense gratification (avirati), ...

Alasya - Sloth, inertia of mind or body due to dominance of the tamasic element. Yoga requires discipline, zeal and tapas (will-power) to succeed on its path. Laziness will prevent you from attaining your highest potential.
6.

An ardent enthusiastic student, with Parama Utsaha, Sahasa and Dridhata (zeal, cheerfulness and tenacity), can effect Siddhi (perfection) within six months; while a happy-go-lucky practitioner with Tandri and Alasya (drowsiness and laziness) will ...

17- 'Slesmavikaramsca vimsatimata urdhvam vyakh-yasyamah, tadyathatrptisca, tandra ca, nidra-dhikyam ca, staimityam ca, gurugatrata ca, alasyamca, mukhamadhuryam ca, mukhasravasca......svetamutrane travarcastvam ca iti vimsatih slesma vikarah.

See also: Yoga, Body, Mind, Asana, Prana