When I opened this thread I assumed the question was more specific in relation to stress during trading, but it seems yours is more of a general problem.
Certain individuals are more prone to stress than others. Some are calm in most situations while others worry about everything.
I have always been very calm, but I used to have trouble sleeping when I worked very long hours in a physical job right into bed time. My physical body simply needed a long time to switch gears from forward to neutral.
Your problem is likely a combination of physical and mental factors.
Like mentioned, there is no excuse to not do at least some training on a daily basis even if it is just a walk. HIT cardio takes less than 15 minutes. You mentioned exercise being a big part of your life. Did this problem occur after stopping working out?
If so, you know why.
Not a problem for me any longer even when working with problem-solving, but try to avoid working the last hours of the day and see if it makes a difference. Unwind with something that takes your mind off your daily "worries". Spend some time in the sack with your girlfriend, read a book, socialize with friends, listen to beautiful relaxing music (I like classical), a walk in nature, watch a movie, etc.
Further, I suspect that you may be troubled with an over-active mind like very many in this day and age.
Personally, I was very heavily into meditation a few years back and it changed me profoundly. Unfortunately for me, the mediation was related to a religious practice at the time, but you certainly do not have to be religious or sit with your legs in a cross and chant in order to practice.
In it`s most basic form, mediation is a method to practice concentration and a focused mind grounded in the here and now.
You can start with relaxing your body completely from head to toe. This is an exercise in itself and you may get very sleepy. After achieving relaxation, practice meditation by focusing on something. Personally, I think a candle light is very good because it is moving and dynamic. The goal is to simply observe the flame without THINKING.
What you will find, is that it is extremely hard to do this even for 5 seconds. Your mind will be overflowing with a constant flow of thoughts. At this point, you will truly realize how much bullshit is going through your mind at any given moment without having any BENEFIT whatsoever other than agitating you. Keep re-focusing after losing concentration. Try to hold your attention for 10 seconds. What you will find is that you will drift away in daydreams for minutes without even being aware of it.
As you keep practicing this, 10 minutes per day, you will find that you eventually start experiencing long periods of focused concentration and that your mind will start calming.
Extend it to your daily life and practice awareness there also.
I have not practiced dedicated meditation for a while now, but it changed me permanently and I try to practice awareness all day long. For the first 20 years of my life, I kept living long into the future and daydreaming all day long. Now, I rarely think ahead at all.