One way to hold comatose: a body lying so far below the waking surface that nothing you do reaches it. You can say the name, shake the shoulder, turn on the light — nothing comes back. The medical sense is that picture for real. The everyday sense borrows the same picture as a joke about someone flat on a sofa after a huge meal or a long day.
Wiktionary records comatose as coma + -ose ('full of'), with coma from Ancient Greek κῶμα 'deep sleep'. The word therefore names someone filled with that deep sleep.
字源資料把 comatose 拆成 coma（昏迷）加 -ose（充滿…的），coma 又來自古希臘文 κῶμα「很深的睡」。所以整個字就是「被深睡填滿的人」，這條線索正好對上兩個意思共用的畫面。
Wiktionary/kaikki extract supplied in this evidence packet (source_ref kaikki:3f6f69a190036ae4:782730507): 'Equivalent to coma + -ose (full of)'.
Two branches
醫學上的昏迷
這一支就是核心畫面本身，沒有比喻：重病或嚴重受傷之後，人真的沉在意識之下，叫不醒。
adjective · C1
In a coma: so deeply unconscious after a serious illness or injury that the person cannot be woken, and cannot speak, move or answer you. The state can last hours, days or much longer.
昏迷的
誇張的癱軟
把醫學的畫面整個借過來誇張用。說話的人知道對方沒事，只是用最重的字形容「動都不動」。
adjective · C1
Lying completely still and not reacting to anything, because you are very tired, very full, fast asleep, or have drunk too much alcohol. The speaker is exaggerating: the person is not really in a coma.
累癱的／癱著不動的