彼は横にばったり倒れた。

he; him; his; boyfriend

topic marker particle; indicates contrast with another option (stated or unstated); adds emphasis

horizontal (as opposed to vertical); lying down; side-to-side (as opposed to front-to-back); width; breadth; side (of a box, etc.); beside; aside; next to; unconnected

at (place, time); in; on; during; to (direction, state); toward; into; for (purpose); because of (reason); for; with; by; from; as (i.e. in the role of); per; in; for; a (e.g. "once a month"); and; in addition to; if; although

with a clash; with a thud; with a bang; with a flop; plump; unexpectedly (meeting someone); suddenly (ending); abruptly (coming to a halt)

to fall; to collapse; to drop; to fall senseless; to be forced to bed (by illness, etc.); to die; to go bankrupt; to be ruined; to have a bad debt; to be defeated (in a game); to fall (of governments, dictators, etc.)