While passed out can mean being soundly asleep, properly it refers to someone who is unconscious.

Is passing out considered sleeping?

Fainting is not the same as being asleep or unconscious. When a person faints, it's usually temporary and the person can be revived in a few minutes. Someone who is unconsciousness, however, won't respond to attempts to revive him.

What does get passed out mean?

When someone “passes out” it means that they become unconscious for a short time. This could be from illness, tiredness, heat, emotion or alcohol. Another verb for this is "to faint".