Overthink - to think about something too much or for too long.
Dwell on - to think or talk a lot about something, especially something it would be better to forget.
Anxiety - the state of feeling nervous or worried that something bad is going to happen.
Obsessive - thinking too much about one particular person or thing, in a way that is not normal.
Mindfulness - a mental state achieved by concentrating on the present moment, while calmly accepting the feelings and thoughts that come to you, used as a technique to help you relax.
Distraction - a thing that takes your attention away from what you are doing or thinking about.
Wellbeing - general health and happiness.
Technique - a particular way of doing something, especially one in which you have to learn special skills.
Definition of overthink from the Oxford Advanced Learner's Dictionary[
How to get the excess out of your head