Likely cause
People tend to overthink in there free time. It could be because of Constant stress from personal or professional life.
What to watch for
If thoughts are of self harm or triggering then it's a red flag, you shouldn't avoid these signs. Constant stress will lead to further disease like IBS or ulcers so see professional health early.
What you can do
Try to be with people you love, talk to them. Surround your self with people when thoughts are high. Keep your self busy and engage in activities which will keep your mind distracted from those disturbing thoughts.
When to see a doctor
Seek help immediately if thoughts are Constant and of self harm or suicidal. There is special helpline for that and just know that there is nothing that can't be solve.
This is general information from a verified doctor and is not a diagnosis or a substitute for an in-person consultation. In an emergency, seek immediate medical care.