From Wiktionary, the free dictionary
не́рвя се (nérvja se, “to be anxious, nervous”) + -ак (-ak).
нерва́к • (nervák) m (feminine нерва́чка)
- (colloquial) nervous, restless, jittery person
- “нервак”, in Речник на българския език [Dictionary of the Bulgarian Language] (in Bulgarian), Sofia: Bulgarian Academy of Sciences, 2014
- “нервак”, in Речник на българския език [Dictionary of the Bulgarian Language] (in Bulgarian), Chitanka, 2010