One way to picture convulsion: something gripped and shaken hard from the inside, jerking in , with nobody able to hold it still. The first thing shaken is a sick person's body. the same picture and the thing shaking can be a country, the ground under it, or a room full of people who cannot stop laughing.
From the word’s history
Wiktionary gives Latin convulsio, from the verb convello. The packet does not gloss that Latin verb, so the link between the Latin root and the shaking picture is left here as a suggestion rather than a claim.
Wiktionary 記錄這個字來自拉丁文 convulsiō，動詞形是 convellō。packet 沒有給出那個拉丁動詞的字義，所以這裡只把「猛力扯動」的畫面當成一個好記的想法，不當成已證實的詞源說明。
Wiktionary entry 'convulsion' (kaikki extract, source_ref kaikki:3f6f69a190036ae4:458880574:16673); etymology_text supplied in this packet reads: From Latin convulsiō, from convellō.
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