+1 for the gym/pool if inclined.
If you simply just want to chill and don't have the energy due to workload for exercise (remembering when I was working a 55-60hr week for about 4 years here myself...) I would suggest the following.
1. Perhaps re-frame your perspective on how you view/react to work.
Example; if you get 250 emails per day, have multiple conflicting projects running concurrently or whatever meaning that you always have several issues to deal with at any one moment of the day such that they creep into your personal life then you need to look at ways of reducing the impact of incessant conflicting demands on your time. Otherwise work (there will never be enough hours in the day period) will increasingly creep into your personal life emanating in Saturday work etc.
Step # 1: Increase your efficiency!
An example, every email I get (crackberry addict here) if it is something you can deal with in less than 2 minutes then I just respond to it immediately (during the work day) and reclaim that mindspace. If it is an update/request or just some info I've been sent but am not looking at/working on currently it gets deleted immediately or diverted/saved in the relevant sub-folder(outlook is great for automating this). Should I end up then working on it I can check it later. You will know yourself if something is important and will react to the first interaction as required.
For example I use my commute to delete a lot of shit and to cover any remaining 2 minute responses before I hit the office.
At the end of each month I take the time to delete/archive any remaining crap in my inbox (lots) that ended up being mere "spam" as no one got back to me.
Step # 1: Prioritize better.
If their email/work was important they will chase me about it, if it was really important to them they will chase me about it a second time. If they send me a third email or call me I respond immediately. This doesn't mean I get to work on whatever they required immediately, frankly I may have other more important things to do - but I will tell them when I will look into it or when they can expect a response from me. It then goes into the calendar and gets done - simple. If it wasn't really important you wont hear from them after their first email/contact (I have learned that much important work isn't really that important).
I have a floating work-pile of perhaps 15-16 things which may need done at any one time. It would be ideal if they were all done yesterday. If I am doing important work for my c-levels it goes high on my list - however if I have something else I really need to get completed at that moment I tell them of this and ask if they can wait. Your boss or your bosses boss often tends to be reasonable as they actually don't want to **** something up further downstream. Generally if it is work that could decrease or head off future work that should go high. If it is "high value" work or perhaps for an important client then high. You get the gist
The point is be RUTHLESS and realize that your time is precious. If implemented correctly you will get to a point where upon reflection all of your time was allocated efficiently and was used to resolve the most pressing/important/significant problems for your business and you did not waste time on the trivial. This will get noticed.
2. Perspectives on Stress.
Stress and pressure or visible work strain/effort can have significant impacts on your health and your career.
# 1: Ask yourself why are you getting stressed?
Seriously, what are you worrying about? People get stressed about things they often shouldn't. I really mean that last sentence!! Follow this if you will. I honestly do not get annoyed, stressed or angry about most of the bollox that other people do. My train is late - so what. Someone else at work has seriously **** something up - oh well. Those Americans have elected a shitty president once again - surprise, surprise etc and so on. I may have opinions about these or other things but I do not get stressed/angry or annoyed with them. But why you may ask? Quite simple; if it is not something about which I/you have some direct control over, can influence, or can directly affect oneself - such as my current haircut, the quality of my work etc then **** it frankly. If I have created something sub-par or of poor quality then I have a right to be angry with myself if I choose so. Otherwise why on earth should I worry about something over which I have absolutely no control? Ergo I don't - ever!! Are any of these things causing the work-stress out of your sphere of direct influence/control? Can you ignore them? If not who then should you talk to to change them?
Once you get past this noise and focus on those things which you can directly affect how then do you deal with these lesser remaining stresses/pressures? If you are not dealing with them seek assistance.
# 2: Are you doing too much?
I'm going to take a guess and say yes as you seem stressed. Now think of some of your more effective colleagues or managers (if applicable). Do they over-work? Do they seem stressed? Generally there is a close correlation between the two. A good manager knows how to effectively manage stress, a high-pressure workload and get results. A really good manager knows how to manage stress, a high-pressure workload, get results and have a personal life. The best do all of this by managing expectations up and down the food chain and so can garner and deploy resources ever more effectively. It's the same for most employees. Whatever your situation do you need help? Does anyone know?
No need to await a major event until they find out - say you need assistance if they expect anything further of you given your current workload. People will keep piling and stacking more work until they receive push-back or resistance.
# 3: Not breaking.
Are you taking your lunch break or some other form of time-out during the day. Take it - leave the office if you have to!
Are you being remunerated for the extra work or working late etc. Send a few responses to the bosses emails if you are working particularly late - though sparingly as it will ruin the myth of your effortlessness. It will be noticed trust me - then request more money/bonus etc given your efforts and book a holiday.
If people are completely unaware of your extraordinary efforts then why are you actually bothering? Seriously if there is no recognition and there is unlikely to be any for it then **** it. If you are hoping they will recognize when you move position and someone else takes on your current role then oh dear... the future is uncertain. I wouldn't bank on it.
# 4: Switch off.
As you seem unable to switch off under your own volition you need to select an arbitrary time each evening - perhaps when you leave work - after which you will not undertake any work related activities. Thinking is exempt obviously - but no actual bloody work. And damn well exclude your weekends! Realizing after a few days that you will be unable to action any work (irrespective of how much you think of it) will hopefully end up with you being more easily able to dismiss such thoughts after a few days.
You will notice that I haven't actually given you any recommendations on how to actually relax/chill in the evenings. This is because quite honestly you need to treat the causes of and not the manifestations of the issues.
NB: Two pieces of info I found interesting. The fact you are living alone (otherwise irrelevant to general issue) and no alcohol. I read this sort of like a freudian slip and will take a wild guess and say you are most likely an introvert who isnt socializing enough. Even introverts need to socialize so perhaps look for ways to increase your social interaction outside work.
Personally I like to pick up random women at salsa class.