People have felt into overthinking acts without even knowing how, when, and why. It is so obvious that different people have been trapped into an overthinking situation over an issue of life (relevant or irrelevant).
You mind be thinking for a long period without knowing that you are into it. It happens curiously and in a blink of an eye when the mind (heart) gets upset or worried about single or multiple things. You might be enjoying yourself possibly for a long time and suddenly heard about or something pops in your mind, then your mind will in a very short time (within some second) got trapped into thinking.
You will start thinking in a bit of slow motion. You will keep thinking and that particular thing would start deviating your mind and concentration to thinking of it. At that early stage of thinking, you won’t recognize or even recall how you started till you overthink for some time.
The real and factual reason on why you think to overthink stage is that “the particular issue or subject matter that pop to you and started thinking on the concern you (it is important you)”. That doesn’t mean it must concern you directly or matters you most, it might be possible one of yours (like maybe family, siblings, neighbors, society, province, country, or even Government).
It would be hard for you or find out someone overthinking something that doesn’t concern or relate to him/her. Whatever strived your mind to overthinking level, you will find out that particular thing concerns you and your entire life. You can’t just be thinking deeply for a long time on something that doesn’t concern you in all life terms – most of the things we heard about or that pop up in our mind are mostly related to our life.