Why to waste ones vauable time finding out various definitions for stress. To overcome stress or to prevent stress to overcome ones self, the best way is to practise "Pranayam". Only "Anulom Vilom" , "Bhramari" and " Udgeeth"; it is enough if you practise it with dedication 15 minutes each pranayam daily early in the morning with empty stomach but after completinng your routines upto morning bath; of course you can have little warm (slightly) water during the practice, only if feel thursty. By doing this you can prevent stress, even depression(critical stage with suicidal tendency). But remember, you have to practise it regularly. Instead of eating away thousands worth medicines (I will call it poison) for whole life why can't you spend only a few hours daily for this best medicine from the God Almighty... Oxygen is freely available without any cost in the surroundings itself. No investments required for this pranayam practice. Thanks... God bless you friends