A stun and sleep both function exactly the same way.
Neither can be applied if the status already exists.
Both disable you from moving or retaliating. [Loss of character control]
Both disable you from pursuing a target.
And both allow your enemy to apply status effects to you without you being pulled from the status.
The only difference is that Stun and Sleep differ in when the status effect expires.
Stuns are short duration that naturally expire and allow the agitator to continue attacking.
Sleep will end if any direct damage is placed into the affect target of sleep, but last longer.
Thematically, a 'sleep' is a state of unconsciousness. So is a stun. The difference is one is a state of natural unconsciousness, the other being a forced state from some type of trauma [when regarding stun in combative terms].
So if we want to apply the 'real world' logic that you represent. And take into account that a stun leaving you vulnerable to sequential stuns, then the same is true for sleep. Arguing that a stun should intentionally leave you susceptible to further stuns, means the current 'rested' mechanic should be removed, as being place into a magical but natural state of sleep, leave you open to being kept in that state.