i had a job as a call centre agent about a year ago here in the Philippines for a US based company. That meant us working at night as that is day in the States due to the 12 hours time difference. i used to work all night and but sleeping during the day was just so hard as i had other daily errands to do. that resulted me to not having enough rest, and unknowingly, for months, i was angry and stressed, very irritable. i did not know why until i quit my job and had a good sleep. i had my happiness back, all over again. Sufficient amount of sleep is vital .