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.
From the word’s history
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)'.
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