[sevensor]

In practice the two will be impossible to tease apart at any rate. Stress and lack of sleep make a feedback loop. The more you feel like you're drowning, the harder it gets to find sleep. Adding nighttime feedings just throws gas on the fire.

[WalterSear]

From a fine grained point of view, yes, stress causes sleep problems.

However, stress is a result of, and not the cause of the sleep deprivation that comes with nursing and changing a child throughout the night.