die Unruhe
restlessness
A state of inner nervousness, tension, or restlessness.
Vor der wichtigen Präsentation spürte sie eine wachsende Unruhe.
Before the important presentation, she felt a growing restlessness.

unrest
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restlessness
A state of inner nervousness, tension, or restlessness.
Vor der wichtigen Präsentation spürte sie eine wachsende Unruhe.
Before the important presentation, she felt a growing restlessness.

The word is made up of the prefix 'Un-' and the noun 'Ruhe' (calm/rest). The prefix 'Un-' expresses the opposite, so 'Unruhe' (unrest/restlessness) is literally the absence of calm.
Die laute Musik störte die Ruhe im Haus.
The loud music disturbed the peace in the house.
You can recognize the meaning from the context: inner 'Unruhe' (restlessness/nervousness) is often felt or sensed. Political 'Unruhen' (unrest) are usually plural and break out. The 'Unruhe' (balance wheel) in a watch or clock is a technical term.
Vor dem Examen spürte ich eine große innere Unruhe.
Before the exam, I felt great inner restlessness.
For the state of nervousness, phrases such as 'innere Unruhe' (inner restlessness), 'Unruhe stiften' (to deliberately cause unrest), or 'jemanden in Unruhe versetzen' (to unsettle someone) are typical.
Die Nachricht von seiner Kündigung versetzte das ganze Team in Unruhe.
The news of his dismissal unsettled the whole team.
In the context of turmoil, people often speak of 'politischen' or 'sozialen Unruhen' (political or social unrest). Typical verbs are 'ausbrechen' (to break out) or the phrase 'es kommt zu Unruhen' (unrest occurs / breaks out).
Wegen der hohen Preise kam es zu sozialen Unruhen im Land.
Because of the high prices, social unrest broke out in the country.
This meaning of 'Unruhe' (balance wheel) as a watch or clock component belongs to watchmakers' technical language and is very rare in general usage.
Nur ein Spezialist kann die Unruhe einer so alten Uhr reparieren.
Only a specialist can repair the balance wheel of such an old clock.
quiet / calm
'die Ruhe' and 'die Unruhe' are opposites here. 'Ruhe' means inner calm and relaxation, especially when you are not nervous or stressed. 'Unruhe' means inner nervousness, tension, or the feeling that you cannot stay calm. They can be confused because both talk about a person's inner state. Pay attention to the prefix 'un-': it turns Ruhe into its opposite.

Im Krankenhaus spürt sie eine starke Unruhe, weil sie auf die Nachricht wartet.
In the hospital, she feels a strong restlessness because she is waiting for the news.
Vor der Prüfung versucht Max, seine Ruhe zu bewahren.
Before the exam, Max tries to keep calm.