I never felt asleep,When I am watching TV.But when I am studying or listening to Dhamma, sometimes I have felt asleep. What may be the cause of this ? But I can say, if I am falling asleep while watching TV,it is because of tiredness.
How can we stop become sleepy by developing Sati? ( I read the advice from Lord Buddha to Arahant Moggollana to overcome sleepiness.But I need to know the cause of sleepiness and how to prevent it before it arises)