英和和英

indulge in fantasies

to indulge in idle fancies―indulge in day-dreams―build castles in the air

an idle indulgence in fantasy

have one's head in the clouds

contemplate one's navel

the action of daydreaming about something

to have an illusion

fanciful―fantastic―visionary―chimerical―moonshiny―Utopian―Quixotic

to indulge in idle fancies―indulge in day-dreams―build castles in the air

labor under a delusion

to give rein to one's fancy―give a loose to one's fancy

be lost in (a) reverie

be lost in contemplation

be lost in thought

wrapped in thought

have the idea that…＝get the idea into one's head that…

deep in meditation

to be sunk in meditation

be under the delusion that ...

have a daydream

of a person, to be lost in one's thoughts

have an obsession that…

be lost [absorbed, buried] in thought