If you're often snapping awake at the dreaded 4am, peering into the pitch black with a mix of frustration and intrigue, it could be down to more than just an annoying quirk in your sleep routine. It might seem a simple habit, but the truth is that there might be an underlying cause worth paying attention to. Lisa Artis, deputy CEO of The Sleep Charity , which has collaborated with Simba mattresses, has this to say about our sleep cycles: "We start to experience less deep sleep after around four