Sleep is typically broken by any attacks. How do passive damaging abilities like necrophos's or radiance burn affect sleeping units? Do they cause them to wake up or not?
Anything that is damage will break the effect. Unless the unit is also affected by invulnerability from Naga Siren's ultimate, in which case, no damage, no waking up.
HP removal effects such as Necro's aura or wave of terror will not break sleep, will not break clarities or salves, however they will do damage through invulnerability effects such as Naga Siren's ultimate.