If you wanted to, could you really get away from work? That sounds like a stupid question, but it's not.
In theory, when you walk out the door at five o'clock (or six, or eight o'clock) your time is your own, to spend with your family or your friends, to read a good book or watch a movie, to see a play or work on your knitting.
But you know how it goes:

• Your cell phone rings and your supervisor needs you to come in right now to look into a system crash.
  
• You feel that you have to check your Blackberry every ten minutes to see if you have any important messages.
  
• You feel a strange impulse to stop in at the next Starbucks just to log into your email to see if there are any crises that need you.
  
• Your secretary tracks you down at your vacation cabin at the beach to ask where the presentation files are stored.
  

It's getting harder and harder to actually disconnect from work, and may people feel that work has a call on them at all times - that they're never allowed to disconnect.
Sociologists call this "work/life permeability" and there's a ton of research on its causes and its bad effects.
I can summarize the research simply:

• Being unable to disconnect from work at all means that you can never really relax and get perspective on your job - you're always in the battle.
  
• If your boss can always call you, then there's never any time that you can promise your family to be available; and that weakens family bonds over time.
  
• Part of the blame goes to our wired society and the communication devices that have become so necessary to you: cell phones and pagers and laptops.
  
• Part of the blame goes to the business environment, which really does run 24 by 7 by 12 and experiences crises at inconvenient times.
  
• Part goes to the new attitude of business that they're paying you a salary rather than by the hour, so they have a claim on your entire day.
  
• And part of it goes to your own vanity, which wants to be reassured that you're indispensable to the business and that they can't get along without you.
  

None of these should be surprising, except the last one - that you are, in part, responsible for the electronic chains that connect you to work.
Don't beat yourself up about this, it's part of being human and wanting to belong to a community - but you've carried it a little too far.
So to fix this problem your're going to have to

• Break all the electronic ties when you really want to get away: leave the cell phone at home, don't carry the Blackberry or laptop.
  
• Tell your boss firmly that you're on vacation and you won't be available, even for emergencies, and then stick to it.
  Threaten your secretary if she tries to locate you at the mountain hideaway.
  
• Examine your own feelings about how much energy you owe to work and how much to yourself.
  When you've reached your own answer to that question, start to live as though you believed it

You can expect that it will be difficult to break the habit at first and it will feel uncomfortable to be disconnected and on your own, but it's important and you'll start to feel recharged so that you can be that much more effective when you get back to work.