Under which of the following sleeping postures is Wudu NOT broken?

Ablution (الوضوء): Invalidators (نواقص الوضوء) Part 2

• Sleeping flat on one's back.
• Sleeping while sitting firmly with both buttocks seated flat on the ground.
• Sleeping while prostrating (Sujud) in prayer.
• Leaning against a wall such that removing it would cause him to fall.