I couldn't sleep last night and so i took 5mg melatonin and zzzquil. is that ok to do?

Duplicate therapy: Melatonin and Nyquil products both contain substances that cause sedation. Combining such products can produce excess sedation which is dangerous for some people, especially those on medications such as Xanax (alprazolam).

Depends: Melatonin may or may not work for many people and thus you should try the long-acting type for a few days before adding anything or stopping its use when there has been no benefit. zzzquil , Dramamine, and Xanax (alprazolam) all cause some drowsiness and thus it is unwise to take them together. However if you were to use on zzzquil and melatonin alone, this'd be ok.

No: it's best not to mix and match medications.