This noun denotes sleeplessness or wakeful watching—nights spent alert rather than sleeping. In 2 Corinthians, Paul lists it twice among his apostolic hardships: sleepless nights endured in ministry service (6:5, 11:27). These are not mere insomnia but purposeful vigilance—nights spent in prayer, care for the churches, or circumstances that prevented rest. The word captures both the physical deprivation and the devoted watchfulness that marked Paul's ministry. It's the toll of apostolic labor: nights awake in prayer, anxiety for the churches, or dangerous circumstances requiring alert vigilance.