I fully understand what you are saying and for those of you saying "you are having too hard a pace", I 'm not sure I agree that is always the case when people get burned by this process. Even though keeping track of all your progress IS a good thing, it can itself also be a stress factor (and not keeping track can be it aswell), not that your boss/PM will be on you if they see something is not going according to plan, but for yourself. Just having this logged info is something that WILL make most people work just that little little bit harder than you normally would ALL THE TIME and I'm not sure putting more time on your time estimates will fix this for everyone. I don't think a motivator (which your burn down chart is) is always positive.
Some people won't feel this way, others will. There is not ONE way of work that WILL fit all. Never will be IMO.
Also, if you say that the idea of these types of agile methods and sprints is not becoming more effective/productive, why should you even use it at all? Why do you think companies want to use these methods at all? It's not because it is fun...
Effectivity/productivity always comes at some type of price, IMO. It doesn't pop up from nowhere just by using the magic methods if you get my point.
The only way for you to become more effective (work and pressure wise) and do less work is make someone else do the work or by automating it.
IMO one should always review ones processes and see what can be automated and spend time on automating your processes instead. Automation comes at the price of doing extra work instead of doing "the real work" but no matter how small the automated task you will always profit in the long run. ALWAYS! If not one day, in two. Not one month, two. Not one year, in two years. You get the idea.
However, I like the idea of having time off to work on personal projects. Most companies will never allow this though. But perhaps you can persuade your employer to get this time to automate your processes and this work could be "outside of sprint control" to allow the time you are talking about to "rest" and get energy back for a new sprint.
Those were just my 2 cents. I get a bit frightened when people say these methods aren't here to make us more effective and work harder. Ofcourse they are! When you have no trace of what you are doing you will rest when your body tells you to. When "everything" you do is traced, you will push yourself. Or I correct myself, most people work this way, some will rest anyway.