Is deep thoughts/thinking a mental illness? If so, is there a name for this illness?

It is perfectly normal to be a big thinker or to have deep thoughts, it is good to think things through, but what to look out for would be if they become intrusive on your daily life, or if they become dangerous (as in acting towards yourself or others). If you think this is happening, it is good to reach out to a friend or listener to talk some of the thoughts out and see if maybe there is something going on underneath the thoughts. Sometimes deep thinking is a good way to process things that have happened to you or around you, it gives you time to fully comprehend everything and make a good choice in your reaction.