Brief Answer:
Natural techniques to be tried first

Detailed Answer:
Hello and welcome to Ask A Doctor service.

Over-thinking being the only symptom could just be stress. Stress can be induced by some disease, some external factors like arguments, etc. Best is to drink lots of water.
Breathing techniques and meditation are some natural methods to deal with over-thinking. Art of Living has many meditations on youtube that you can practice. Otherwise you can learn and do it at home by yourself.

Hope this helps. Let me know if I can assist you further.
Dr Vaishalee

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