Atom Smasher said:
Seems to me you have lost (or never had) the desire and/or ability to give your thoughts boundaries and you let them run away into infinity. Therefore they are your master.
Maintaining sanity involves creating a reality and working within the structure you have created. When you let your thought run hog-wild, there is no structure, no reality, only despair.
Use life, don't let it use you. You must create structure and demand that your thoughts serve you. Get over that vague feeling of there being something wrong with limiting your introspection.
Take it from someone who used to be just like you. Or reject it. Your choice.
Agreed x1000.
In my adolescence I viewed existence and the world through very sh!te-coloured pessimistic goggles. I would spend hours constantly over-analyzing the minutest of things, heading further and further down the spiral. I would read bleak and fatalistic books (Brave New World was my favorite for years) which although being amazing works of art only contributed to this outlook.
Somewhere around 18 I delved into philosophy. I decided to break these shackles of pessimistic perception and master my reality. Yes, this at times involves limiting the runaway train of over analysis and reminding yourself of the self-realized and adopted foundation of your chosen reality.
Slightly random but I only did psychedelic drugs two times. One time I accidentally took a substantially larger dose than intended and the trip went a dark direction and tried to gain mastery over my objective reality. It was difficult but I kept mentally returning to the foundation or reality I had carefully and painstakingly built over years. I believe the experience would've been much, much worse if I hadn't spent those years carefully honing and refining MY philosophy and MY reality. Although not involving drugs, your OP predicament sounds similar.
Start reading a lot (Not SoSauve, but philosophy, ideology, history, etc) and see what makes sense to you man. Reality is perception, so define what you want yours to be and proceed. It's a long road and I'm certainly still on it.