to shut oneself in (e.g. one's room); to be confined in; to be filled with (emotion, enthusiasm, etc.); to fill the room (of a gas, smell, etc.); to be heavy with (e.g. smoke); to be muffled (e.g. voice); to hold (a castle, fortress, etc.)
to stay indoors; to be confined indoors
to seclude oneself; to shut oneself away
to barricade oneself in; to hold (a fort, etc.); to shut oneself up; to be besieged; to dig in
to stay bottled up inside oneself; to be introverted; to have a melancholic appearance, atmosphere (of a person, object, place); to have a gloomy appearance
shutting oneself in (one's room, etc.); barricading oneself in (a fort, etc.) while being besieged; holing up (in a building)
shut-in; stay-at-home; hikikomori; social withdrawal; shunning other people
to seclude oneself; to shut oneself away
to cause heartache because of a (hidden) love; to be miserable because of love