Höfuðverkurinn versnar þegar ég sef illa.

The headache gets worse when I sleep badly.

Breakdown of Höfuðverkurinn versnar þegar ég sef illa.

• ég: I
• sofa: to sleep
• þegar: when
• höfuðverkurinn: the headache

Questions & Answers about Höfuðverkurinn versnar þegar ég sef illa.

Why is höfuðverkurinn written with -inn at the end?

Because Icelandic usually puts the definite article on the end of the noun.

• höfuðverkur = headache
• höfuðverkurinn = the headache

So the sentence literally says The headache gets worse when I sleep badly.

If the English meaning you were shown uses my headache, that is coming from context, not from the Icelandic grammar itself. To say my headache explicitly, you would normally say höfuðverkurinn minn.

Is höfuðverkur a compound word?

Yes. Icelandic uses compound words very often.

• höfuð = head
• verkur = pain, ache

So höfuðverkur is literally something like head-pain, meaning headache.

This is very typical Icelandic word-building, and getting used to compounds helps a lot when reading.

Why is the verb versnar used here, and what form is it?