The sleep watcher by Rowan Hisayo Buchanan

When she is sixteen, Kit suffers a summer of peculiar sleeplessness. Her body lies in bed while she wanders through her family home, the streets of her run-down seaside town and into the houses of friends and strangers. Unseen and unheard, she witnesses her parents and their fracturing relationship. Her home thrums with quiet violence that she can no longer ignore. With this secret knowledge it becomes impossible not to react and a single choice soon changes everything.