Learn Hardcore Greek: Όταν νυστάζω, πλένω το πρόσωπό μου με κρύο νερό. - When I get sleepy, I wash my face with cold water.

Breakdown of Όταν νυστάζω, πλένω το πρόσωπό μου με κρύο νερό.

Why is νυστάζω used here? Is it a verb meaning to be sleepy?

Yes. νυστάζω is a very common Greek verb meaning to feel sleepy / to be getting sleepy.

A native English speaker may expect something like I am sleepy, with an adjective, but Greek often uses this verb instead.

So:

You can also hear adjective-based expressions in Greek, but νυστάζω is extremely natural in everyday speech.

Why does the sentence start with Όταν? Does it mean when or whenever?

Here όταν means when, but in this kind of sentence it often has the sense of whenever too.

Because both verbs are in the present tense, the sentence describes a habitual/repeated action:

So this is not just about one single moment. It describes what the speaker generally does in that situation.

Why are both verbs in the present tense?

Because the sentence expresses a general habit.

In Greek, the present tense is commonly used for repeated actions and routines, just like in English:

If the speaker were talking about one specific past event or one future event, the tense choice would be different.