noun
ball-tightening sensation
Internet slang describing the sudden, visceral tightening of the testicles, often from fear, thrill, or a drop sensation (e.g., on a roller coaster).
See also: ヒュンと
ジェットコースターで急降下したとき、玉ヒュンした。
When the roller coaster dropped, I got that ball-tightening feeling.
高いところから落ちそうになって、マジで玉ヒュンだった。
I almost fell from a high place and seriously felt my balls tighten.
Compound of 玉 (tama, 'balls') and ヒュン (hyun), an onomatopoeia for a swift, sharp movement or sound. The exact origin is uncertain, but it likely emerged in internet communities to vividly describe the sensation of testicles tightening from fear or thrill.