ひょっとすると彼女は重い病気かもしれない。

possibly; perhaps; perchance; unintentionally; accidentally

if; when; and; with; particle used for quoting (with speech, thoughts, etc.); quoting particle; promoted pawn; indicates question (sentence end)

she; her; her; girlfriend; sweetheart

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

heavy; weighty; massive; heavy (feeling); depressed; gloomy; blue; uneasy; slow; sluggish; lumbering; ponderous; clumsy; important; serious; grave; serious; severe; critical; solid; established; dignified; sensible

illness; disease; sickness

may; might; perhaps; may be; possibly

to become known; to come to light; to be discovered; to be known; to be understood; to obviously not amount to much; to seem trivial; to be evident; to be obvious; to go without saying; to be very intense (worry, hope, etc.); to be extremely severe