All 90 nervous kaomoji here have a sweat drop, and some are shaking. The drop is usually a semicolon. The shake is extra brackets. Tap a face and it is copied. Twenty-five need only a keyboard, (^_^;) among them.
Read the full guide
Pick how nervous, then tap
Tap a tile and that face is copied. The groups run from mild to bad: smiling through it, a blank stare, wide eyes, shaking, then hands that wipe a brow or press together. Search reads the labels: sorry finds eight faces, the deep bow m(_ _;)m among them, and exam finds (；-人-) and (；・_・) 緊張.
What the semicolon is doing
It is a sweat drop. Wikipedia's article on kaomoji calls (-_-;) a generic emoticon for nervousness, and says an apostrophe or a quotation mark can do the same job, the way a drop is drawn in manga: (^_^') and (^_^") are both here. 67 faces use Semicolon, U+003B, and 20 use Fullwidth semicolon, U+FF1B.
Tips
Keyboard only keeps the 25 faces made of plain ASCII. ^^; is the shortest, at three characters.
Twelve faces say it in Japanese. Wiktionary gives dokidoki as with a racing heart and hiyaase as cold sweat.
More brackets, more shaking: ((；・_・)) is a shiver and (((；ﾟДﾟ))) is the whole body.
Questions and answers
What does (^_^;) mean?
A smile with a sweat drop on it: nervous, embarrassed, awkward. Wikipedia's list of emoticons files (^_^;) under nervous, embarrassed, troubled and shy, beside (-_-;), (・_・;) and ^^;. All four are on this page.
How do you type a nervous kaomoji on a keyboard?
Open bracket, caret, underscore, caret, semicolon, close bracket: (^_^;). Leave the brackets off for ^_^; or add a second semicolon when things get worse. The Keyboard only chip shows all 25 that need nothing else.
What does m(_ _)m mean?
A bow with both hands on the floor. Wikipedia's list of emoticons gives m(_ _)m as a kowtow for respect or a dogeza for apology. The one here, m(_ _;)m, adds a semicolon, so the apology is sweating as well.