Sleep pressure is essentially the need for sleep that builds up in your body the longer you're awake. It's like a pressure cooker that's gradually increasing in pressure over the course of the day. When you sleep, you release that pressure, and when you wake up, the process starts all over again. Napping can also release some of this pressure, which is why it can potentially interfere with nighttime sleep for some people. If you're struggling with sleep at night, it might be because your naps are releasing too much of your sleep pressure during the day.