obsession

noun

1. (countable, uncountable)The quality of being obsessed.
2. (countable, uncountable)An idea that engenders a compulsive or irrational preoccupation, or the preoccupation thereby engendered.
3. (countable, uncountable)An activity or entity that inspires a compulsive and potentially unhealthy fixation, or the fixation thereby inspired.

   “Editing Wikipedia started as a hobby, but it's turned into a complete obsession of mine.”

4. (countable, uncountable)Influence or control by evil spirits without possession.

   “if an evil spirit counterfeits the presence of God, and comes upon the man as an influence only, it may be described as obsession; but when a footing is gained in him, it is "possession," because the obsessing spirits have gained access, and possess the ground they hold, up to the extent of the ground given.”

   “They should see that a perception of their identification with the Victor of Calvary is absolutely necessary if they are to constantly and victoriously resist the obsession of evil spirits.”

   “It is true, that by the workings of the law of attraction, and the susceptibility of mortals to the influence of spirit powers, mortals may become obsessed by the spirits of evil—that is evil spirits of men who once lived on earth—and this obsession may become so complete and powerful that the living mortal may lose all power to resist this influence of the evil spirits...”