There are a few explanations for this:

1. Awakenings are estimations based on continuous movement of your wrist for at least five minutes. It may be that you were restless while asleep, but did not actually awake.

2. There’s evidence suggesting that we sometimes don’t remember brief periods of wakefulness when we reflect on our sleep upon waking. In other words, it’s possible you briefly awoke, but don’t recall it.

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