Lack of iron and/or sleeping.

Nirvana was an American rock band that was formed by singer/guitarist Kurt Cobain and bassist Krist Novoselic in Aberdeen, Washington in 1987. Nirvana went through a succession of drummers, the longest-lasting being Dave Grohl, who joined the band in 1990.

"Nirvana means freedom from pain, suffering and the external world, and that's pretty close to my definition of punk rock." - Kurt Cobain.
Personal Blog.   Come as you are.   We can share our endorphins.