I have never played any pvp where a sleep can last 45 secs

Either have I, including this game- there is no 45 sec sleep.
or can be recasted constantly over and over.

Sleep can be cast over and over, it just takes a cast time (that can be interrupted after swiftcast and nightwing) and diminishings begin exponentially on the 2nd cast and the target will become immune. No sense in casting over and over and usually this is impossible even if I wanted to due to casting time, the bounty on my head, and interrupts and stuns.