cataplexy

Concise Oxford English Dictionary © 2008 Oxford University Press:
cataplexy /ˈkatəˌplɛksi/

▶noun a medical condition in which strong emotion or laughter causes a person to suffer sudden physical collapse though remaining conscious.

– derivatives
cataplectic adjective.

– origin C19: from Gk kataplēxis ‘stupefaction’, from kataplessein, from kata- ‘down’ + plēssein ‘strike’.