Once I get stuck into a state like this it becomes my normal. I somehow fail to recognize that I am in this state, and I slowly drift out of touch with reality. It's like I start skimming over the present moment. This clouded state of being can go on for months without me recognizing that I'm wrapped up in it. And to me anyway, this is a source of anxiety. It feels almost like a state of frenzy. My mind's cogs and wheels will be working overtime to solve some perceived problem which I never seem get to the bottom of. It just keeps going.
This is where perspective gets lost. My world becomes my thoughts. My reference points aren't based on reality anymore, they come from these imagined thoughts. This is why some people are said to be living in "fantasy land". Controlled correctly, imagination can be a great thing, as long as you don't overindulge and remember to "return to reality" ie the present moment every now and then. But a lot of people's imagined thoughts are of a fearful, anxious nature. It's like being stuck in a storm of thought where you forget what peace and calm feel like.
This peace and calm is what many people call "Zen" I suppose. But when I look at sportsmen, it must be what "being in the zone" is. You hear golfers talk about the feeling of "being the ball" while hitting a winning put shot. Their mind is COMPLETELY quiet. They are at peace. Thoughts about "missing the shot" or "oh no, the world is watching me" don't enter their mind at all. They are 100% focused on that little ball. This "being in the zone" is something that I am very fascinated by.
The other end of the spectrum encompasses a wide range of mental disorders in my opinion. When I see a "mentally disturbed" person walking down the street talking to themselves, I am almost certain that they are suffering from extreme addiction to obsessive over thinking. They get to point where they cannot see their way out.
Thoughts create feelings. If you have obsessive thoughts of a fearful nature, your body and self will be filled with fear and anxiety. If this carries on for months and months and maybe years, you will no doubt feel depressed and anxiety ridden. I have first hand experience of this. It is nearly impossible to see anything outside of this state. It is like being lost in the woods. If you have overly obsessive thoughts about making money, those thoughts will keep triggering that "lust for money" feeling. This feeling will keep fueling the over thinking but it isn't true peace and calm, which is what this person is after I'm sure. "Once I make my money, I will be happy".
The way to really experience peace and calm is to "let go" of your thoughts. The best way in my opinion is to focus using your senses. A lot of meditation teachers like to focus on the breath etc. This is fine but I suspect that a lot of people might find this boring and be turned away from it. I like to focus on "busier things". More exciting things. Like watching a sports match. I will see how long I can maintain my focus before I drift away into my thoughts. When I realize that I have been thinking about something else (for like 5 or 10 minutes sometimes!) I return to present observation. Going deeper and deeper into observation. This produces profound effects. You might come across this while reading a book. At the end of a page you might think to yourself "What the hell was I reading!" and have to read it again. The key is to try and sustain your attention for as long as possible, while going as far "into" the object of your attention. It provides an intense feeling of calm. Try it!