preoccupation
n.n. a strong interest or worry that takes up most of your time and energy. You use this when you are thinking about one thing so much that you cannot focus on anything else.
n. a state of being deeply absorbed in a particular thought or concern. Often implies a singular focus that excludes other matters from the mind.
His constant preoccupation with work made him a poor friend.
The politician's preoccupation with the upcoming election left little time for the daily management of the city's infrastructure.
The novel explores the protagonist's preoccupation with her past, suggesting that her inability to move forward is the root cause of her current emotional distress.
Borrowed from Middle French préoccupation, from Latin praeoccupātiō. By surface analysis, pre- + occupation or preoccupy + -ation.