From catching some Zs. Catch + Z = Zatch, meaning to sleep. For people who have been living inside a catsup dispenser for the last ten decades, Zs apear over sleeping cartoon character's heads. Example: 3 AM already. Fforget the term paper. I gotta go zatch for a while.
ZATCH
Meaning of ZATCH in English
Slang English vocab. Английский сленговый словарь. 2012