Hi, Over thinking refers to the process of repetitive unproductive thoughts.
When you are over thinking you might feel like your brain won't shut off.People who have the tendency to worry so much are usually more anxious than normal people.Stress ,lower self esteem,lack of support from others, perfectionism,etc are some reasons for over thinking .
When you're in anxiety and depression we ruminate on the thoughts without letting it go.
You cannot control your thoughts, learning to deal with those thoughts is important .
Next Steps
Consult a psychologist.There are various techniques which help you to avoid overthinking .
Health Tips
Keeping yourself busy, Mindfulness meditation,etc will help you.