The reasons for not being able to sleep can be quite diverse. It might be that you're excited about an upcoming event, or maybe you have a lot on your mind and can't stop thinking. Another possibility is that your body's internal clock is out of sync. For example, if you take naps during the day or go to bed at irregular times, it can mess up your sleep pattern.
There could be many reasons. Maybe it's stress, or too much caffeine. Sometimes an uncomfortable sleeping environment can also cause it.
It's often because the scary elements get stuck in your mind and make you anxious or nervous, keeping you from relaxing enough to sleep.
Maybe it's because the comics are too exciting and keep your mind active.
It could be due to stress or an irregular sleep schedule. Maybe there is a comic that explores this issue, but I'm not sure.
Maybe they were too stressed or had a noisy neighbor. That could prevent them from sleeping.
Maybe the bear is too excited or worried about something. That could keep it awake.
Maybe it's haunted by some past events or fears. That could keep it awake.
One classic can't - sleep story is 'The Three Little Pigs'. The story of the three little pigs building their houses, one of straw, one of sticks, and one of bricks, and the big bad wolf trying to blow them down is engaging. It has enough suspense and a happy ending that can soothe your mind. Another could be 'Goldilocks and the Three Bears'. The idea of Goldilocks exploring the bears' house and getting into all sorts of situations is both interesting and can take your mind off your sleeplessness.
Maybe it's too personal and has a deep impact. It could be tied to emotions or significant experiences that make it hard to let go.
One possible reason could be the stress of his ninja duties. He has so many missions and responsibilities that his mind is constantly racing, making it hard to relax and fall asleep.
Maybe the little bear is too excited or has a lot on its mind.