"Aτυχία" is just bad luck. But, "δυστυχία" is the general feeling of sadness.
"Παραμονή" is staying at a place for a matter of time, while "διαμονή" is the accommodation.
Also, "παραμονή' is the "eve", e.g. "Παραμονή Πρωτοχρονιάς" (= New Year's Eve).
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Vasiliki Baskou, Instructor/Director, https://learn-greek-online.com.