My mind never seems to switch off. Even when nothing is wrong, I lie awake at night running through everything that could go wrong tomorrow. Is this normal, or is something wrong with me?
What you are describing, a mind that keeps running long after the day is done, is something many people experience, and it does not mean something is wrong with you. Worry is the mind's way of trying to stay safe by preparing for problems in advance. The difficulty is that at night there is nothing to act on, so the thoughts simply circle.
A few things tend to help. Keeping a regular sleep and wake time gives the body a rhythm to settle into. Writing the worries down earlier in the evening, on paper, can tell the mind that they have been noted and do not need rehearsing at midnight. Slow breathing, where the out breath is a little longer than the in breath, gently signals the body that it is safe to rest.
If the worry is present most days, is hard to control, and is affecting your sleep, work, or relationships over several weeks, that is worth taking seriously, and it is a good reason to speak with a doctor or a mental health professional. Persistent, excessive worry of this kind is common and treatable. You are not weak for finding it hard, and you do not have to manage it alone.